Tutorial Complete

Petroleum Experts

User Manual

IPM TUTORIAL October 2009

2

Copyright Notice The copyright in this manual and the associated computer program are the property of Petroleum Experts Ltd. All rights reserved. Both, this manual and the computer program have have been provided pursuant to a Licence Agreement containing restriction of use. No part of this manual may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language, in any form or by any means, electronic, mechanical, magnetic, optical or otherwise, or disclose to third parties without prior written consent from Petroleum Experts Ltd., Petex House, 10 Logie Mill, Edinburgh, EH7 4HG, Scotland, UK. © Petroleum Experts Experts Ltd. All rights reserved. IPM Suite, GAP, PROSPER, MBAL, PVTP, REVEAL, RESOLVE, IFM, ModelCatalogue and OpenServer are trademarks of Petroleum Experts Ltd. Microsoft (Windows), Windows (2000) and Windows (XP) are registered trademarks of the Microsoft Corporation The software described in this manual is furnished under under a licence agreement. The software may be used or copied only in accordance accordance with the terms of the agreement. It is against the law to copy copy the software on any medium except as specifically specifically allowed in the license agreement. No part of this documentation may be be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or information storage and retrieval systems for any purpose other than the purchaser's personal use, unless express written consent has been given by Petroleum Experts Limited.

Address: Petroleum Experts Limited Petex House 10 Logie Mill Edinburgh, Scotland EH7 4HG Tel : (44 131) 474 7030 Fax : (44 131) 474 7031 email: [email protected] [email protected] Internet: www.petex.com

© 1990-2009 Petroleum Experts Limited

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Copyright Notice The copyright in this manual and the associated computer program are the property of Petroleum Experts Ltd. All rights reserved. Both, this manual and the computer program have have been provided pursuant to a Licence Agreement containing restriction of use. No part of this manual may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language, in any form or by any means, electronic, mechanical, magnetic, optical or otherwise, or disclose to third parties without prior written consent from Petroleum Experts Ltd., Petex House, 10 Logie Mill, Edinburgh, EH7 4HG, Scotland, UK. © Petroleum Experts Experts Ltd. All rights reserved. IPM Suite, GAP, PROSPER, MBAL, PVTP, REVEAL, RESOLVE, IFM, ModelCatalogue and OpenServer are trademarks of Petroleum Experts Ltd. Microsoft (Windows), Windows (2000) and Windows (XP) are registered trademarks of the Microsoft Corporation The software described in this manual is furnished under under a licence agreement. The software may be used or copied only in accordance accordance with the terms of the agreement. It is against the law to copy copy the software on any medium except as specifically specifically allowed in the license agreement. No part of this documentation may be be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or information storage and retrieval systems for any purpose other than the purchaser's personal use, unless express written consent has been given by Petroleum Experts Limited.

Address: Petroleum Experts Limited Petex House 10 Logie Mill Edinburgh, Scotland EH7 4HG Tel : (44 131) 474 7030 Fax : (44 131) 474 7031 email: [email protected] [email protected] Internet: www.petex.com


I

Contents

Table of Contents 0

Chapter 1

2

Introduction

1 About This Guide ................................................................................................................................... 2 2 How to use this ................................................................................................................................... guide 2 Symbols and conventions ..........................................................................................................................................................

Chapter 2

3

5

Dexterity Examples

1 GAP Gas Network ................................................................................................................................... Example 5 Objectives

..........................................................................................................................................................

5

Learning topics .........................................................................................................................................................

6

Executive summary .........................................................................................................................................................

6

STEP 1 : Initialise .......................................................................................................................................................... GAP

6

STEP 2 : Define.......................................................................................................................................................... GAP System Options

8

STEP 3 : Define .......................................................................................................................................................... GAP Model Schematically

10

STEP 4 : Define .......................................................................................................................................................... the Well

11

STEP 5 : Calculate .......................................................................................................................................................... the Well IPR and VLP

13

STEP 6 : Define .......................................................................................................................................................... pipeline

17

STEP 7 : Solve .......................................................................................................................................................... the GAP Network

18

STEP 8 : Material .......................................................................................................................................................... Balance Prediction

19

STEP 9 : Constraints ..........................................................................................................................................................

24

2 PROSPER Gas ................................................................................................................................... Well Example 31 Objectives

..........................................................................................................................................................

32

Learning topics .........................................................................................................................................................

32

Executive......................................................................................................................................................... Summary

32

STEP 1 : Initialise .......................................................................................................................................................... PROSPER

32

STEP 2 : Define .......................................................................................................................................................... PROSPER Method/Options

34

STEP 3 : Define .......................................................................................................................................................... fluid PVT Data

34

STEP 4 : Define .......................................................................................................................................................... Well Inflow and Equipment data

35

3 MBAL Gas Reservoir ................................................................................................................................... Example 43 Objectives

..........................................................................................................................................................

44

Learning topics .........................................................................................................................................................

44

Executive......................................................................................................................................................... Summary

44

STEP 1 : Initialise .......................................................................................................................................................... MBAL

44

STEP 2 : Define .......................................................................................................................................................... MBAL Method/Options

47

STEP 3 : Define .......................................................................................................................................................... PVT Data

48

STEP 4 : Define .......................................................................................................................................................... Tank Parameters

49

4 GAP Gas-Lifted ................................................................................................................................... System Example 50 Objectives

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..........................................................................................................................................................

51

Learning topics .........................................................................................................................................................

51

Executive......................................................................................................................................................... summary

51

STEP 1 : System .......................................................................................................................................................... Setup

52

Starting a......................................................................................................................................................... New File

52

GAP options ......................................................................................................................................................... setup

52

Units setup .........................................................................................................................................................

54

Injection fluid ......................................................................................................................................................... setup

55

STEP 2 : System .......................................................................................................................................................... schematics

56

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II

IPM Worked Examples

Adding Wells .........................................................................................................................................................

56

Tie-backs.........................................................................................................................................................

57

The Platform .........................................................................................................................................................

58

Pipes/Links .........................................................................................................................................................

58

Other Drawing ......................................................................................................................................................... Options

60

STEP 3 : Describing .......................................................................................................................................................... the wells

61

Well models .........................................................................................................................................................

62

Generating ......................................................................................................................................................... IPRs From Existing PROSPER Well Models

63

Importing......................................................................................................................................................... Existing Vertical Lift tables to the Well Models

65

STEP 4 : Describing .......................................................................................................................................................... the Pipeline network

67

Riser Description .........................................................................................................................................................

67

'Tie One' ......................................................................................................................................................... Pipeline description

69

‘TieTwo’ Pipeline ......................................................................................................................................................... description

70

STEP 5 : Calculate .......................................................................................................................................................... Production given total lift lift gas available

70

STEP 6 : Results .......................................................................................................................................................... analysis

73

5 Associated Water ................................................................................................................................... / Gas Injection Model Example 77 Objectives

Chapter 3

..........................................................................................................................................................

77

Learning topics .........................................................................................................................................................

78


78

STEP 1 : Set the .......................................................................................................................................................... Production Model

78

STEP 2 : Create .......................................................................................................................................................... the Water Injection Model

81

STEP 3 : Link.......................................................................................................................................................... the Production and the Injection System

84

STEP 4 : Performing .......................................................................................................................................................... the Material Balance Prediction

87

Associated Gas .......................................................................................................................................................... Injection Model

92

Physics Examples

95

1 PROSPER Gas ................................................................................................................................... Lift Example 95 Objectives

..........................................................................................................................................................

95

Learning topics .........................................................................................................................................................

96


97

STEP 1 : Model .......................................................................................................................................................... Setup

97

STEP 2 : Well .......................................................................................................................................................... Model Validation and Data Quality Check

110

STEP 3 : Gas.......................................................................................................................................................... Lift Design

122

STEP 4 : Use.......................................................................................................................................................... of QuickLook Diagnostic tool for gas lift performance validation

127

2 PROSPER ESP ................................................................................................................................... Example 131 Objectives ..........................................................................................................................................................

131

Learning......................................................................................................................................................... topics

132

Executive ......................................................................................................................................................... summary

133

STEP 1 : Model .......................................................................................................................................................... Setup

133

STEP 2 : Well .......................................................................................................................................................... Model Validation and Data Quality Check

142

STEP 3 : ESP .......................................................................................................................................................... Design

146

STEP 4 : Use.......................................................................................................................................................... of QuickLook Diagnostic tool for ESP lift performance validation

153

3 MBAL Gas History ................................................................................................................................... Matching Example 162 Objectives ..........................................................................................................................................................

162

Learning......................................................................................................................................................... topics

162

Executive ......................................................................................................................................................... summary

162

STEP 1 : Initialise .......................................................................................................................................................... MBAL

163

STEP 2 : Input .......................................................................................................................................................... Production History Data

163

STEP 3 : Introduction .......................................................................................................................................................... to Material Balance concepts

165

STEP 4 : Material .......................................................................................................................................................... Balance History Matching

166

STEP 5 : Relative .......................................................................................................................................................... Permeability Matching

172

4 MBAL Oil History ................................................................................................................................... Matching Example 179

III

Contents Objectives ..........................................................................................................................................................

179

Learning......................................................................................................................................................... topics

180

Executive ......................................................................................................................................................... Summary

180

STEP 1 : Model .......................................................................................................................................................... Setup

180

STEP 2 : Matching .......................................................................................................................................................... to Production History data in MBAL

188

STEP 3 : Sensitivity .......................................................................................................................................................... Analysis

195

STEP 4 : History .......................................................................................................................................................... Match Quality Check

197

5 MBAL Production ................................................................................................................................... Prediction Example 198

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198

Learning......................................................................................................................................................... topics

199

Executive ......................................................................................................................................................... Summary

199

STEP 1 : Production .......................................................................................................................................................... Prediction Setup

199

STEP 2 : Boundary .......................................................................................................................................................... conditions

200

STEP 3 : Well .......................................................................................................................................................... Type Definition

201

STEP 4 : Inflow .......................................................................................................................................................... Performance

203

STEP 5 : Outflow .......................................................................................................................................................... Performance

207

STEP 6 : Well .......................................................................................................................................................... Schedule

209

STEP 7 : Reporting .......................................................................................................................................................... frequency

210

STEP 8 : Production .......................................................................................................................................................... prediction

211

IPM Tutorials

III

Chapter

1

Introduction

1

2

Introduction This document contains tutorials for the Petroleum Experts’ software: PROSPER, MBAL and GAP. The tutorials are designed to guide the user through a number of program examples. As a new user, the tutorials provide a good overview of the programs' functionalities and will assist in developing proficiency in use of the tools. The tutorials are split into two sections. The first set of tutorials is designed for new users and it focuses on the dexterity required to use the programs. The second set of tutorials provides more depth and knowledge on use of the tools in achieving various modeling objectives and the physical and engineering concepts related to these.

1.1

About This Guide The guide assumes one is familiar with basic Windows operations and terminology. The screen displays used in this guide are taken from the examples provided with the software. On occasion, the data files may vary from the examples shown as updates to the program are issued. Where major amendments or changes to the program require further explanation, the corresponding documentation will be provided. What is in this guide:

·

Chapter 2, ‘Dexterity Examples’, contains tutorials that concentrate on basic use of the programs, without much detail about the physics of the engineering models addressed

·

Chapter 3, ‘Physics Examples’, contains tutorials that provide more information about the physics of the engineering models addressed

All completed example files can be found in C:\Program Files NOTE: \Petroleum Experts\IPM 7.x\Samples\Worked Examples\Dexterity Examples\ GAP. Please note that the files will be in the form of an archived GAP file (GAR file). The GAR file contains all the necessary models i.e., PROSPER, MBAL, VLP's, etc., that are required to compete the example file. To access the files, the GAR file must first be extracted using the following work-flow: from the main menu of GAP select: File | Arc hive | Extract. Once the GAR file has been extracted, a new instance of GAP can be started and the associated files linked using the tutorial work-flows

1.2

How to use this guide New users to Petroleum Experts ’ IPM software should work through all the examples in Chapter 2 before moving on to Chapter 3. © 1990-2009 Petroleum Experts Limited

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Users proficient in Petroleum Experts IPM software may find the tutorials in Chapter 3 useful.

1.2.1

Symbols and conventions

Throughout the user guide, special fonts and/or icons are used to demonstrate specific steps, instructions and procedures in the program. PETEX program ALL CAPS Italics

Used to highlight information.

certain

points

o

Keycap

Bold fonts are used to indicate a specific action to be taken. For example: ‘Click Done to exit the window.’

Menu Command

To avoid repeating the phrase ‘Click the File menu and choose the Open command’, we use the File|Open convention instead. Emphasizes specific information to be entered or be aware of. This keyboard icon marks step-by-step instructions. This symbol is a reminder to click the RIGHT mouse button. Clicking the righ mouse button performs specific functions in MBAL, depending on the active dialogue box or plot. If you do not have a right mouse button, holding down the SHIFT key while a click on the mouse button performs the required function.

ò

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The term PETEX program is used when the comment is applicable to PROSPER, MBAL or GAP. Represent DOS directories, file names, and commands.

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Chapter

2

5

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Dexterity Examples This section contains the following tutorials: GAP Gas Network Example:

This example builds a simple onshore gas network integrated model and calculates production from the system in time (production prediction). The well model associated with the integrated model is designed in PROSPER (PROSPER gas well example) and the reservoir model associated with the integrated model is designed in MBAL (MBAL Gas reservoir example). PROSPER Gas Well Example:

An example that illustrates gas well modeling in PROSPER. The PROSPER well model is used within the GAP Gas Network example. It can also be run in isolation. MBAL Gas Reservoir Example:

An example that illustrates gas reservoir modeling in MBAL . The MBAL reservoir model is used within the GAP Gas Network example. It can also be run in isolation. GAP Gas Lift Example:

This example illustrates the design and optimization of an oil production system using gas lift. All the example files are located in: C:\Program Files\Petroleum Experts\IPM 7.x\Worked Examples\Dexterity Examples

2.1

GAP Gas Network Example This tutorial example is designed to provide a step-by-step introduction to the GAP program. The emphasis is on the data required to model and analyse the production potential of a dry gas reservoir (no condensate). The actual data is of little importance and for ease of understanding has been chosen to be minimal. However, the systematic approach to building a GAP model using PROSPER well models and MBAL reservoir models is an important element of the tutorial. The PROSPER well modeling and MBAL reservoir modeling phases are separate modules referenced from this GAP tutorial.

2.1.1

Objectives

The system to be modeled is described below:

· An onshore gas field is depleted by a well and producing through a pipeline to a · IPM Tutorials

separator (pressure of 1300psig). Pipeline is 10,000ft in length with an internal diameter of 6inches. October, 2009

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· The well is 17, 350ft deep. · Fluid is dry gas with no condensate or free water associated with it. Objectives: · Calculate production capacity of the system · Calculate production capacity of the system if the separator is constrained to a gas rate of100MMscf/day. 2.1.1.1

Learning topics

This section focuses on how to:

· Design a simple integrated oil production model in GAP · Associate valid well models in GAP · Associate valid reservoir/tank models in GAP · Calculate system potential · Optimise system production to honour a constraint 2.1.1.2

Executive summary

Steps taken to achieve the modeling objective is as follows:

· Describe integrated model schematic in GAP · Construct a well model in PROSPER - VLP and IPR models. · Design a reservoir/tank model in MBAL · Define pipeline model in GAP · Calculate production from the integrated model at a point in time - Solve network · Perform a production prediction · Add a new well and calculate production from the system while honouring separator limit. 2.1.2

STEP 1 : Initialise GAP

This section describes how GAP is started and how the location of the required associated files is initialised. Start GAP by using the following Windows commands: Start | All Programs | Petroleum Experts IPM 7.X | GAP. See the GAP manual for more details on how to start GAP. The version of GAP being used may be checked by selecting, Help | Ab out GAP.


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The command options ( File, Options etc.) on the GAP main menu are laid out in a logical order (left to right; top to bottom fashion) that reflects the order in which operations will usually be performed. Click on File | Directories and check that PROSPER and MBAL Executables point to the current versions of PROSPER and MBAL respectively. The PROSPER and MBAL applications can also be found in the Petroleum Experts directory.

Please note that files saved with these versions of GAP, PROSPER and MBAL will not be readable by previous versions. It is recommended, therefore, that the File | Directory | GAP and MBAL Data Directory options are set to point to directories that are exclusively used to store data files created with the current software versions. When GAP is started a new file is created (unless otherwise specified in the preferences). Create a new file by selecting File | New or using the toolbar icon to start a new file. It is important to ensure that consistent units are used throughout the integrated model, particularly when data generated by PROSPER and MBAL are incorporated into a GAP model. Oilfield units will be used for this example. Select Options | Units to view the units used by GAP for input and output, the data validation ranges, and IPM Tutorials

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output precision. Near the top of the screen within the tabular heading select Oilfield for both input and output units (as shown in Figure 3), and then select OK.

Figure 3: Oilfield Units for Input and Output 2.1.3

STEP 2 : Define GAP System Options

In this section the scope of calculations and general options required for the GAP model will be defined. This example is focused on a dry gas reservoir producing to a separator through a delivery pipeline 10000 ft away. No production history is available, but the fluid volume and composition of the reservoir has been estimated, allowing a material balance prediction to be performed. Select Options | Method to set the GAP calculation method.


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Set System type to Production, Optimisation method to Production, PVT Model to None and Prediction method to Pressure and temperature. Set Prediction type to On. This tells GAP how to update reservoir pressures during a Prediction calculation. A constant reservoir pressure can be specified by selecting None, in which case no prediction calculations are performed: in this case, the model represents the system at an instant in time and no tank models are required. Optimisation may be performed for both predictive (depleting reservoir) and nonpredictive (constant reservoir) calculations. The completed options interface is shown above. This completes the GAP calculation method set-up. Select OK to return to the main GAP window.

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2.1.4

10

STEP 3 : Define GAP Model Schematically

In this section schematics of the gas production system is designed in GAP. This will include all the components/ elements of the integrated model. The properties of the components and reservoir fluids are entered at a later stage using PROSPER and MBAL. The model will consist of a reservoir (specified as a tank), a gas production well and a pipeline connecting the well manifold to the delivery pipeline. It is recommended that the GAP model be specified from the separator (delivery pipeline) end towards the reservoir, allowing complex models to be built easily. Since this example is very simple it makes little difference in what order the components are created. The toolbar ( ) is used to create and modify components on the network schematic. Note that when they are selected they remain active until they are unselected. The exception to this is the ‘Delete’ icon, which must be selected for each deletion. To identify an icon, hold the mouse cursor over it until a yellow box appears with a short description of the icon function. Select the Add Separator icon and click the left-hand mouse button in the main GAP display area towards the top right. The element is labelled 'Separator'. The label is not required, but it is advisable to identify the nodes this way. A separator is considered by GAP to be the end of the production chain or a fixed pressure point in the system. This does not have to represent a separator in reality; rather a node/ point in the system where a known pressure exists. Next, select the Add Joint icon and add a joint. Label this ‘Manifold 1’. Place the manifold to the left of the separator. Place a second “Manifold 2” to the left of this. A joint is any manifold or intersection where pipes converge. A pipe element is defined in between two joints. Select the Add Well icon Select the Tank icon

and add a well below the Manifold 2. Label this ‘Well’.

and add a Tank, named ‘Tank’ below the well.

The elements shall be linked together with the Add Link icon by dragging the lefthand mouse button between two components. The connections are made in the direction of fluid flow. Connect the Tank to its Well, and the Well to its wellhead (Manifold 1). Connect manifold 1 to 2 for the pipe and finally connect Manifold 2 to the Separator. Note that a pipe component has been inserted between the two Manifolds. No pipe components are defined between the Tank, Well, and Manifold 2 since any piping between these components is assumed to be implicitly defined by the Well. Deselect the Link icon to prevent adding more links.


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The basic model layout has been defined: additional components can easily be added or deleted as the model is refined later. The GAP integrated model schematic is shown below

Save the GAP file (using File | Save As) as Gasres.gap in a directory of choice.

2.1.5

STEP 4 : Define the Well

In this step the physical characteristics of the well and reservoir which define flow from the reservoir to the wellhead (‘Manifold’ in this example) shall be specified. The performance of well is defined by a VLP and IPR model. Please refer to the well section of the GAP manual for more details on well models and available options. Although data may be entered directly into GAP, PROSPER will be used to generate the well properties. The main advantage of using PROSPER is that the VLPs and IPRs can be generated later by automatic batch calls to PROSPER from GAP. ‘VLP/ IPR Intersection’ shall be selected as the well model in GAP. In addition, well model validation (i.e. matching model to production history) and sensitivity analysis on different design parameters or future condition of the well can be performed using PROSPER. Double click using the left-hand mouse button on the Well component in the GAP model. A well summary screen is displayed where well type and well model to be IPM Tutorials

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used are selected. All elements contained in the model are listed on the right and data entry for any component can be made by selecting the required component with a left mouse click. A red cross besides the equipment indicates that insufficient data has been entered. Within the Well data entry screen change the Well Type to Gas Producer (this will change the well colour on the main display screen from green to red). Set the well model as VLP / IPR Intersection. Set the rate model as 'Use volumes'. Rates (for the VLPs) can be defined using volumes or mass More information is available under 'Well summary screen' section of GAP manual.

Select the “ Run PROSPER” button in bottom right hand corner and GAP automatically launches a PROSPER file. Check that the correct version of PROSPER is loaded, otherwise check File | Directory from within GAP. Go to the PROSPER Gas Well Example to set up the PROSPER model. Go to the PROSPER Gas Well Example now – Initialise PROSPER.

With the PROSPER well modelling exercise completed, save the file and return to It is GAP from PROSPER by selecting GAP from the main PROSPER menu. recommended that any changes made to a PROSPER file are saved before returning to GAP. On returning to GAP after creating the PROSPER file the PROSPER.OUT file will © 1990-2009 Petroleum Experts Limited

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automatically be placed in the GAP well summary screen PROSPER file path location. Alternatively, use the Browse button to locate the PROSPER.OUT file. The *.out (e.g. Gasres.OUT) PROSPER file should be used in preference to the input (Gasres.SIN) and analysis (Gasres.ANL) files. With the well file path defined, the status becomes valid. To further check that the PROSPER file is properly located select Run PROSPER and return to GAP by selecting GAP on the PROSPER main menu. Select OK to return to the GAP main window. Save the GAP file by clicking on the save icon the overwrite confirmation.

2.1.6

or File| Save and selecting Yes to

STEP 5 : Calculate the Well IPR and VLP

The Inflow Performance Relation (IPR) and Vertical Lift Performance (VLP) data can now be generated automatically by batch calls to PROSPER. The inflow performance relationship (IPR) of the well has been described in the PROSPER well model. We need to transfer the IPR from PROSPER to GAP. For gas wells, while importing the IPR from PROSPER to GAP, GAP takes three points from the PROSPER IPR, and fits the three points to the Forcheimer Pseudo Pressure IPR model or C & n IPR method (Defined by user in the IPR screen of the well in GAP). From the main GAP main menu select Generate | Generate Well IPR's with PROSPER | All | Generate. PROSPER will automatically be called from GAP and pass the IPR and PVT data to the GAP well IPR data section. The process is displayed below.

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Click on All to select all the valid wells in the model (in this case only one).

Figure 10: Select wells message

Click on Generate to proceed and the IPR will be generated (copied across from PROSPER).

Click OK and go back to the main screen. Double-click on the Well icon to bring up the well summary screen then select IPR tab to display the fluid PVT properties, layer pressures and temperatures obtained from PROSPER. Click on the More tab (still in red).


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IPM Tutorial Manual

GAP needs to know how water cut and GOR (case of oils) will evolve in future and

for this pseudo-relative permeability curves are required. For this example, fractional flow rel perms shall be obtained "from tank model". Select this option and the IPR becomes valid. Alternatively, selecting Validate will also remove the red invalid IPR designation. Generate Well VLP's from GAP From the main GAP menu select Generate | Generate Well VLPs with PROSPER | All | Data to specify the ranges of data for which the VLP curves should be generated. PROSPER is called up to load the sensitivity values already stored within it (if any). Enter the following sensitivity values:

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Note that the P o p u l a t e buttons can be used to create the tables rather than the data being entered manually. Data required is as follows: - Liquid rate: 1 - 150MMscf/day (Geometric spacing) - Manifold pressure: 1300 - 10000 psig (Linear spacing) - CGR: 0 and 0.1 stb/MMscf - WGR: 0 - 100 (Linear spacing)

This table covers the range of possible gas production rates, manifold (well head) pressures and water to gas ratios (WGR) that the well may encounter during a prediction. Since the gas is dry with a CGR of zero, the CGR will always be at this value. However a minimum value of 0.1stb/MMscf CGR (negligible) is required by multiphase flow correlations for their calculations. Hence 0 - 0.1stb/MMscf CGR is input for VLP curves generation. Select OK and then Generate to perform the calculations using PROSPER: this may take some time. Select OK | OK when the calculations have completed. Go back to the main screen. Note that the well is now valid as the thick red circle around the well has now disappeared. Double-click on the Well icon to bring up the well summary screen. Notice also that the colour of the VLP and IPR buttons have now turned green indicating a valid GAP well model.


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Now save the GAP file by clicking on save icon confirmation.

2.1.7

and selecting Yes to the overwrite

STEP 6 : Define pipeline

The pipeline profile and equipment data will be input in this section for pressure drop calculations along the pipe. Double click on the pipeline in the GAP model using the left-hand mouse button and select Input at the bottom of the screen, followed by the Description tab, leaving the Environment properties at their default values for pipeline temperature calculations. Enter the following pipe data: Length = 10000 ft TVD downstream = 0 ft TVD upstream = 0 ft Inside diameter = 6 INS Roughness = 0.0006 INS

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Select OK to return to the main screen.

2.1.8

STEP 7 : Solve the GAP Network

This section describes how to calculate production from the integrated model. This objective is achieved by solving the network with the separator pressure boundary condition defined. The potential of the system at a point in time is obtained through this approach while MBAL calculations will provide reservoir pressure decline with time for prediction calculations. Double-click using the left-hand mouse button on the GAP well model. Note that all of the Data Summary flags are green and the Well has a green tick next to it in the list of components on the right side of the Equipment Data Entry screen. If this is not the case, then the VLP and IPR models have not been calculated correctly and STEP 5 should be repeated carefully. To calculate the system production, select Solve Network from GAP menu. Set the Separator Pressure to 1300 psig. Select Next | Calculate. Go back to the main screen when calculation is completed. The results of a network solve can be obtained by hovering the mouse over each network element/node as shown below. Among information displayed are: Qoil; Qwat; Qliq; Qgas; Pressure; Temp.; and dP for the exit point of that item. © 1990-2009 Petroleum Experts Limited

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The results can also be viewed by selecting Results | Detailed | All Items. The gas production rate from the system is 72 MMscf/day. Select OK to return to the main GAP window. Save the GAP file by clicking on save icon confirmation.

2.1.9


STEP 8 : Material Balance Prediction

In this section a tank model is defined using MBAL, and a material balance prediction of flow and pressure decline is undertaken. Go to the MBAL Gas Reservoir Example now - Create the Tank. MBAL will be activated directly from GAP by Double Clicking on the tank and then select Run MBAL from the bottom right hand corner of the Summary Screen as shown below.

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If MBAL has been accessed from GAP, upon returning to GAP from MBAL, the path of the MBAL file will be displayed in the Tank Summary Screen of GAP. If the MBAL file has been prepared by running MBAL standalone/independently, then the file path can be specified by clicking on browse to locate the Gasres.mbi file. Note that the Tank component on the right side of the Equipment Data Entry screen now has a green tick beside its name. On the GAP main screen, there shall be no red circles around the tank or the well. This indicates that all the data is valid. The GAP main screen is as shown in the following figure.


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The material balance tank model is now in place and a prediction can be performed. A simple prediction will be run first, with no constraints or events occurring during the production. This is essentially the same as the Solve Network calculation performed previously, except that a material balance calculation is performed after each time step to update the reservoir pressure and PVT properties. Select Prediction | Run Prediction and set the following time control data.

· Start Date · End Date · Step Size

01/01/2005 01/01/2020 1 Year(s)

Select Next | Next and input a Separator pressure of 1300 psig. Select Next | C alculate and allow the Solve Network cycle to be performed for each of the 15 time steps requested.

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Select Main to go to the main interface when the run is completed. The results of the prediction calculation can be viewed by selecting from the main GAP menu Prediction | Plot Nodes Prediction Results , and highlighting the Separator, Manifold 1 and 2 and Well nodes from the resulting list. Since the components are all in series, the flow parameters should be identical for each node and curves should overlay.


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Click on Plot and a plot window will appear. Select Variables and plot the Gas rate against time. Also plot Water rate, Reservoir pressure and Cum Gas Production results.

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The initial and peak gas rate should be 72 MMscf/day, and the peak water rate should be 44 STB/day. This water is the vaporised and connate water produced as the reservoir depressurises, water expands and formation rocks contract. Select M ain to return the main GAP window. No constraints have been entered in this system, and it is always recommended that none is entered until the potential of the system has been established. At this point the user should consider design options and sensitivity analyses. Now save the GAP file by clicking on save icon confirmation.


This concludes the first objective of the exercise: calculating the system production in time.

2.1.10 STEP 9 : Constraints

This section explains how to achieve the second objective of the exercise: a constraint will be applied to the maximum flow rate that can be passed through the separator. Production from one well is not enough to meet the target rate constraint. However, the use of two wells gives a production much higher than the target rate. Thus, one of the wells will initially have to be choked back to satisfy the separator constraint.


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Select the well icon

and add a new well next to the current well.

The already defined well properties (VLPs, IPR, PVT etc) can be copied to the new well by holding the Ctrl key down while selecting the first well with the left mouse button, and dragging the mouse over the new well. Add a link between the new well and the Manifold 2 using the link icon, and then deselect the link icon. Alternatively, right click on the first well and select Copy. Right click anywhere in the model and select Paste to paste the copied well. Link the well to manifold 1.

Enter the Summary Data Entry screen for the second well by double-clicking on the well's icon with the left-hand mouse button. Change its label to Well 2 in the top left of the screen, and then click on the green tab labelled dP Control in the lower part of the screen. These buttons are quick links to different screens of equipment input data. Set the “ dP Control” to Calculated. This will simulate the presence of a well head choke that allows GAP to reduce the flow from the well and meet any constraints imposed on the system.

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Select OK. The potentially choked (controllable) well will have a thin red ring around it.


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Input the gas rate constraint at the separator by double-clicking using the left-hand mouse button on the separator icon. Navigate to the Constraints data entry section by clicking on the Constraints tab in the lower half of the Equipment Data Entry screen. Enter a Max gas production of 100 MMscf/day, and then select OK.

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The separator constraint is shown on the separator icon as two inward pointing arrows. This is shown in the figure below.


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Select Solve Network | Next and click on the Optimise with all Constraints option:

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Next Calculate to solve the system with the constraint applied. Click on Main to access the main interface when the calculation is finished. Since there are two wells: one fully open and the other with a wellhead choke (dP control), the optimiser will choke back well 2 to achieve the constraint set at the Separator. To access the results, go to Results | Detailed | All Wells . The Gas production for the two wells can be checked. Use Next to move to Well 2 and note that the production has been choked back to 29 MMscf/day to achieve the constraint at separator. A green rhombus will be seen across the separator indicating that constraint of 100MMscf/day gas rate has been honoured. If this is not visible, the option can be activated by selecting View | Highlight Limiting Constraints from the main menu.

If a prediction run is perforrmed (selecting Optimise with all constraints calculation option), Well 2 will be choked back as long as the potential of the system is greater than the constraint set:


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Save the GAP file using save icon

and select Yes to overwrite the current file.

This concludes the objective of the exercise.

2.2

PROSPER Gas Well Example This tutorial example is designed to provide a step-by-step introduction to the PROSPER program. The emphasis is on the data entry required to model a dry gas producing well for inclusion into an integrated gas system model in GAP. See the GAP Gas Network Example for further details. Since it is hoped that this example will be used as a phase in the GAP Gas Network Example, it is anticipated that PROSPER will have been loaded from within GAP. However if that is not the case, this example can also be run using the standalone version of PROSPER. PROSPER is a single well characterisation/modeling program. Its output is principally

Inflow Performance Relationship (IPRs) and Vertical Lift Performance curves (VLPs). These relations respectively describe the inflow to the well sandface from the reservoir and the outflow from the well sandface to a manifold (or well head) at the top of the well. These pressure and flow correlations are heavily reliant on the PVT (Pressure, Volume, and Temperature) characteristics of the produced fluid. Using Inflow and Outflow, we know the behaviour of the well in terms of the flow rates vs. bottom hole pressures for a given mean reservoir pressure. IPM Tutorials

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In addition PROSPER is equipped with techniques to validate the model by matching known correlations to observed production history and also performing detailed sensitivity analyses.

2.2.1

Objectives


· A naturally flowing 17,350 feet deep well. · Tubing is 17250 feet long (2.992 inches ID) with 100 feet of casing (6 inches ID). · The reservoir is at 11500psig and 230degF. · Fluid is dry gas with no condensate or free water associated with it. Objective: · Design a PROSPER well model for input into GAP gas integrated modeling exercise. · Calculate production capacity of the well. 2.2.1.1

Learning topics


· Design a simple well model in · Calculate production. 2.2.1.2

PROSPER.

Executive Summary


· · · · · · 2.2.2

Define PROSPER well modeling options/objectives Define fluid PVT model Define well completion data Define reservoir inflow performance Calculate production from the well Save file for inclusion into GAP gas integrated production model.

STEP 1 : Initialise PROSPER

If PROSPER has not been started from GAP, it can be run standalone using the following Windows commands: Start | All Programs | Petroleum Experts IPM 7.X | PROSPER. See the PROSPER manual for more details on how to launch PROSPER. It is necessary to check that the current version of PROSPER has been loaded. The © 1990-2009 Petroleum Experts Limited

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version of PROSPER being used can be seen in bottom right hand side of main PROSPER interface or by selecting Help | About Prosper . The command options ( File, Options etc.) at the top of the PROSPER window are laid out in a logical order (left to right; top to bottom fashion) that reflects the order or workflow required to design well models. Select File | New to start a new file if required. PROSPER has been launched from GAP.

This step is not necessary if

Note that files saved with this version of PROSPER will not be readable by previous versions. Select File | Preferences followed by the File tab. It is recommended that the Default Data Directory field is set (using the Browse button) to a directory that is exclusively used to store data files created with the current software version. This is as shown in the following figure.

Select the Units tab. It is also important to ensure that consistent units are used throughout, particularly when data generated by PROSPER may be incorporated into an MBAL or GAP model. Oilfield units will be used for this example. Ensure that Input Units and Output Units box have Oilfield selected. Select Done to return to the main PROSPER window.

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34

STEP 2 : Define PROSPER Method/Options

In this section the well modeling objectives in PROSPER are set e.g. well type, fluid type e.t.c. Detailed information about these options will be entered later. This example is focused on a dry gas producing well. Select Options | Options to display the System Summary screen. The Options interface defines the well modeling objective and based on this, the necessary data interfaces become active in the model. Set the options shown below and click Done. NOTE: The modeling Options required will automatically be set if PROSPER was activated directly from GAP.

2.2.4

STEP 3 : Define fluid PVT Data

An unmatched Black Oil PVT model shall be employed for fluid characterisation. Select PVT | Input Data to enter the PVT data. Note the options to match Black oil correlations to measured data, or to use PVT data lookup tables. If lookup tables are used, data covering the range of temperatures, pressures and GOR/CGR which may be encountered by the well is required. Enter the following data and select Done. Gas gravity 0.59 Separator pressure 100 psig Condensate to Gas Ratio 0 STB/MMscf


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Condensate gravity Water to Gas ratio Water salinity Mole Percent H2S Mole Percent CO2 Mole Percent N2

50 API 0 STB/MMscf 10000 ppm 0% 0% 0%

Though a condensate gravity of 50 degAPI is specified, this is not used in calculations since a CGR of zero is input. However a value of 5 degAPI or greater is required by default. See the PROSPER manual on details of how to change unit range defaults.

2.2.5

STEP 4 : Define Well Inflow and Equipment data

This step defines the properties of the reservoir and well that will determine the flow rate of the produced fluid for a given reservoir pressure and well head pressure. Select System | Equipment (Tubing etc) to input the well properties. Select All, and then Edit. Enter the following deviation survey data describing a vertical well profile down to a depth of 17350 ft. Click Done when the deviation survey data has been entered. Measured Depth (ft)

True Vertical Depth (ft)

0

0

17350

17350

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No surface equipment is required in this model. Note that all equipment between the well head and manifold defined in GAP would in general have to be input here so that the various pressure drops due to these equipments are accounted for in the VLP. Select Cancel. Enter the following tubing and casing data in the downhole equipment screen, and then click Done. Type

Measured depth (ft)

Inside diameter (in)

Roughness (in)

X’mass tree

0

-

-

Tubing

17250

2.992

0.0006

Casing

17350

6

0.0006


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A temperature profile for the well is required. This is defined by a temperature model selected under System Options. Please see section of PROSPER Userguide for more information on temperature models. This model is performing a pressure and temperature calculation, therefore the temperature of the surrounding formations and a mean heat transfer coefficient are required. Enter the following linear geothermal gradient and then select Done. Measured Depth (ft) Formation temperature ( oF) 0

60

17350

230 Overall heat transfer coefficient 3 BTU/ft2/F/hr

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The fluid average heat capacities shall be left at their default values. Click on Done to accept the values. Back on the main Equipment data entry screen. Select Summary | Draw Downhole to view a schematic of the downhole equipment. Select Main to save the input data and return to the main PROSPER window.


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The equipment data defined will be used with a VLP correlation function for estimation of pressure drops in the well (i.e. define the VLP). The next step is to define the well inflow using an Inflow Performance model. In PROSPER main screen, select System | Inflow Performance to call up the IPR IPM Tutorials

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Input screen. Click on the Petroleum Experts Reservoir Model and Enter Skin By Hand for the Mechanical/Geometrical Skin. Set the following data in the lower right of the screen.

· · · ·

Reservoir Pressure Reservoir Temperature Water Gas Ratio Condensate Gas Ratio

11500 psig 230 degrees F 0 STB/MMscf 0 STB/MMscf

Select the Input Data button at the top right of the interface and enter the following data within the Reservoir Model section.

· · · · · · · · ·

Reservoir Permeability Reservoir Thickness Drainage Area Dietz Shape Factor Wellbore Radius Perforation Interval Time Reservoir Porosity Swc

20 md 100 feet 2500 acres 31.6 0.354 feet 30 feet 100 days 0.2 0.2 © 1990-2009 Petroleum Experts Limited

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Select the Mech/Geom Skin tab and enter a skin value of 2. Select Calculate . An IPR plot showing the inflow to the well as a function of the well’s sandface pressure will be shown. An AOF of 143 MMscf/day is shown as the maximum flow obtainable.

Absolute open flow (AOF) for gases in PROSPER is limited to 150MMscf/day and oils to 40,000stb/day by default. If AOF of the well being modelled exceeds these values (i.e. pressure not at a value of zero), the IPR will be truncated. The limits can be changed by going to File | Preferences | Limits and inserting higher values for the AOF. Model validation cannot be performed for this example since no production/ measured data exists for the well. The next step is to calculate the production of the well (VLP+IPR intersection). Select Calculation | System (IPR+VLP) | 3 variables and enter the following data.

· · · · · ·

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Top Node Pressure Water Gas Ratio Condensate Gas Ratio Vertical Lift Correlation Solution Node Rate Method

1500 psig 0 STB/MMscf 0 STB/MMscf Petroleum Experts 2 Bottom Node Automatic - Linear

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An unmatched VLP correlation (Petroleum experts 2) will be used to calculate pressure drops in the well. If test data exists, a suitable correlation can be matched to reproduce the pressure drops in the well in reality and this will be selected here. Select Continue | Continue | Calculate. The production from the system and other parameters are displayed under solution details on the right. Scroll right (towards the bottom of the screen) within the Results display until the dP Friction and dP Gravity columns are shown. Notice that for moderate and large gas flow rates, the frictional pressure drop within the well dominates the gravitational pressure drop to such an extent that these flow rates are unlikely to ever be achieved, suggesting that perhaps a larger diameter well should be considered. Select Plot to display the results.


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The X-axis shows the produced gas flow rate and the Y-axis shows the well sandface pressure. The reservoir pressure has been set to 11500 psig and the well head pressure to 1500 psig. For these pressures, the IPR (green curve) and VLP (red curve) intersect at a well sandface pressure of 8644 psig and flow rate of 72 MMscf/day, these being the flow conditions that the well would actually achieve (i.e. the unique flow pressure solution that lies on both the IPR and VLP curves). Move the mouse cursor within the plot to display the X and Y coordinate values are displayed at the top right of the screen. The relatively steep gradient of the VLP curve compared with the IPR curve indicates that a high percentage of the pressure drop from the reservoir to the well head is as a result of high frictional resistance within the well. Select Finish. Save the PROSPER file as Gasres.out in a suitable directory by clicking File |Save As. If PROSPER was being run from GAP, select GAP on the menu bar to return to the GAP Gas Network Example documentation, otherwise select File | Exit . This completes the PROSPER gas well modeling exercise - Click here to Return to GAP

2.3

MBAL Gas Reservoir Example This tutorial example is designed to provide a step-by-step introduction to the MBAL program. The emphasis is on the data entry required to model a dry gas reservoir for inclusion into an Integrated gas system model in GAP. See the GAP Gas Example

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for further details. MBAL is a reservoir analysis tool that makes use of the production history of a reservoir and the PVT characteristics of the production fluid in performing mass

balance calculations to estimate the original volumes of fluid in place and identify the driving mechanisms acting within the reservoir (e.g. fluid expansion, formation expansion and aquifer inflow). Good PVT characterisation and production history are usually an essential input to an MBAL calculation, but for this tutorial example a minimum of input data is required. With respect to the GAP Gas Example, the purpose of the MBAL model is to define the reservoir characteristics so that material balance prediction calculations can be performed by GAP.

2.3.1

Objectives


· A dry gas reservoir with no condensate or free water associated with it. · The reservoir volume is 600Bscf of dry gas at 11500psig and 230degF. Objective: · Design a MBAL tank model for input into GAP gas integrated modeling exercise. 2.3.1.1

Learning topics


· Design a simple reservoir/tank model in 2.3.1.2

MBAL.

Executive Summary


· Define MBAL reservoir modeling options/objectives · Define fluid PVT model · Input tank parameters for volumes and saturations, initial conditions of pressure · 2.3.2

and temperature e.t.c Save file for inclusion into GAP gas integrated production model.

STEP 1 : Initialise MBAL

If MBAL has not been started from GAP, it can be run standalone by using the following Windows commands: Start | All Programs | Petroleum Experts IPM 7.X | MBAL. See the MBAL manual for more details on how to launch MBAL.


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From GAP the MBAL program can be started from the tank summary screen by clicking on R u n M B A L as shown in the following figure.

When MBAL is launched, the following interface appears.

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Check that the current version of MBAL has been loaded. The version number can be checked by selecting Help | About MBAL Package. From the main MBAL menu select Tool | Material Balance to start an MBAL material balance session. The command options ( File, Tool, Options etc.) at the top of the MBAL window are laid out in a logical order (left to right; top to bottom) that reflects the sequence of operations required to build a valid tank model. Note that files saved with this version of MBAL will not be readable by previous versions. It is therefore recommended that the File | Data Directory option is set to a directory that is exclusively used to store data files created with the current software version. It is important to ensure that consistent units are used throughout, particularly when data generated by MBAL may be incorporated into a GAP model. Oilfield units will be used for this example. Select Units to view the units used by MBAL for both input and output, as well as the expected data ranges. Select Oilfield for both input and output units, and then select Done.


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STEP 2 : Define MBAL Method/Options

In this section the type of reservoir fluid and tank model that fulfils MBAL modeling objective will be defined. Their detailed specification will be entered later. This example is focused on modeling a dry gas reservoir. Select Options to display the System Options screen. The options interface defines the MBAL tank modeling objective and based on this, the necessary data sections become active in the model. Set the options shown in the figure below and then select Done.

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48

STEP 3 : Define PVT Data

An unmatched Black Oil PVT sahll be used for fluid characterisation. Select PVT | F luid Properties to enter the PVT data. Note the options to match Black oil correlations to measured data, or to use lookup tables of PVT data. The PVT data used by MBAL must be the same as that used by PROSPER if an integrated GAP model involving MBAL and PROSPER is to be used. To aid this process, MBAL can import the PVT data used by PROSPER by using the Import button to import a PVT file generated by PROSPER (e.g. GASRES.PVT ) . If this is done, then the same matching to correlations or tabulated values must be initialised within MBAL. Enter the fluid PVT data as shown in the figure below, and select Done. The condensate gravity of 50 API will not be used in calculations since CGR is zero, but a value greater than 5 is required by default. See the MBAL manual for details on how to change unit range defaults. Gas gravity Separator pressure Condensate to Gas ratio Condensate gravity

0.59 100 psig 0 STB/MMscf 50 API © 1990-2009 Petroleum Experts Limited

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Water salinity Mole percent H2S Mole percent CO2 Mole percent N2

2.3.5

10000 ppm 0% 0% 0%

STEP 4 : Define Tank Parameters

This step defines the physical properties of the reservoir required for material balance calculations. From MBAL main screen, select Input | Tank Data to input the tank properties. Input the following parameters within the Tank Input Data screen. The Validate button at the bottom of the screens can be used to validate the data input for each screen. Tank Parameters · Tank Type · Temperature · Initial Pressure · Porosity · Connate Water Saturation · Water Compressibility · Original Gas In Place · Start of Production Water Influx · Model

Gas 230 deg F 11500 psig 0.2 fraction 0.2 fraction Use Corr (1/psi) 600000 MMscf 01/01/2005

None

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Relative Permeability · Rel Perm from · Water Sweep Eff. · Hysteresis

50

Corey Functions 100% No

Residual Saturation

End Point

Exponent

Krw

0.2

0.8

2

Krg

0.01

0.9

1.5

Note that the residual saturation for water corresponds to the connate water saturation. There is no Pore Volume vs. Depth or Production History to be entered. one when the data has been entered.

Select D

With no production history available, production history matching is not possible. Select File | Save As to save the MBAL data. Enter the file name GasRes.MBI and save the file in a suitable directory. If MBAL was being run from GAP, clicking on GAP on the main menu gives the option to return back to GAP. Click on O.K. to return the main GAP interface. If MBAL was being ran stand-alone, select File | Exit to exit the application. In GAP, from the tank summary screen browse to the MBAL file to validate the tank. This concludes the MBAL gas reservoir modeling example. - Click here to return to the GAP Tutorial Now .

2.4

GAP Gas-Lifted System Example The main objective of this example is to show how the non-linear optimisation capability of GAP can be used to optimize the gas lift allocation to gas lifted wells in a simple production system, thereby optimising/maximising the total oil production from the field.


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Objectives

This tutorial offers a guide to setting up of the example, and also an overview of other GAP functionalities that can/will be used to achieve the modeling objective. These points will be made in the body of the text. It is encouraged to navigate through other GAP features as one proceeds through the example as this is a useful way of learning about other features not described here. For more details on a particular feature, please refer to the main GAP manual. The system to be modeled is described below:

· · · · ·

An oilfield has two gas lifted wells: well GL1 and well GL2. Each well is tied back to the riser base via a 1500 ft flowline. Each flowline has an ID of 5 inches. The riser is 500 ft long and has an ID of 10 inches. The platform is at 500 ft above the seabed. The seabed is assumed to be flat.

The objectives of the exercise is to maximise production from a gas lifted oil production system by re-allocating produced gas across the wells in the system using the S o l v e N e t w o r k calculation. NOTE: The model will also include an MBAL tank that is not necessary to have when using the S o l v e N e t w o r k calcualtion, enabling a prediction to be performed if desired once the gas lift optimisation tutorial has been completed

2.4.1.1

Learning topics


· Design a simple integrated gas lifted model in GAP · Associate valid well models in GAP · Associate valid reservoir/tank models in GAP · Calculate system potential · Optimise system production through gas lift allocation to wells 2.4.1.2

Executive summary

The steps required to build the integrated network model are listed below. These generally are the standard steps required and may vary depending on modeling

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objectives (e.g. inclusion of tank models for reservoir perfomance prediction).

· · · · · · · · 2.4.2

Setting up the system Drawing the schematics of the system Setting up the well models Describing the surface network Generating the inflow performances from existing well models Generating lift curves for the wells Optimal allocation of gas lift gas available Analysing the results

STEP 1 : System Setup

This section sets GAP up for construction of the network. The steps are:

· · · · 2.4.2.1

Start a new file. Set up the optimisation method. Set up the units. Set up the gas injection source.

Starting a New File

Select File ½ New to start up a new file. This option clears the current screen display and resets the program workspace to initial values.

2.4.2.2

GAP options setup

To set-up the optimisation method and other GAP options, choose Options | M ethod Select the following input parameters:

·

System type: Production Water and gas injection systems can also be modelled. When performing a prediction run, these injection systems can be associated with a production system to provide voidage replacement (for example) into the producing reservoirs.

·

Optimisation Method: Production Various optimisation methods (e.g. Reveue, heating value e.t.c) are available.

·

PVT Model: Black Oil Please see Section 1.3 of the GAP User Guide for a detailed description of the fluid modeling options.


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·

Prediction: None One can run predictive models in GAP, either using a simple decline curve model or by linking to Petroleum Experts’ MBAL program to perform Material Balance calculations. Connectivity to Petroleum Expert’s REVEAL numerical simulator can also be done.

·

Prediction Method: Pressure and temperature This allows GAP to perform pressure and temperature drop calculations in pipeline models.

·

Water Vapor: No Calculation or Calculate Condensed Water Vapor This option is available for Dry and Wet Gas and Retrograde Condensate fluid types. If the Calculate Condensed Water Vapor option has been set, then the condensation of water vapor will be taken into account in the pressure drop calculations.

·

Temperature Model: Rough Approximation

This is the default temperature model in GAP. GAP uses an Overall Heat Transfer Coefficient specified by the user alongside enviromental temperature conditions and fluid heat capacities, to determine the heat lost by the fluid to the surroundings.

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Select Ok to conclude this step. 2.4.2.3

Units setup

To set-up the input and output units, click on Options | Units and select the unit system required. Clicking on the cell below the Input or Output column header (defaulted to Oilfield) will yield a selectable list of available units systems. Oilfield units shall be employed throughout this example. For more information on units systems in GAP, please refer to the units section of the online help or the GAP manual.


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Click on Ok to complete this step. 2.4.2.4

Injection fluid setup

If the integrated model contains gas injections sources (either gas lifted wells or gas injection into a reservoir model) or any fluid injection source, the fluid characteristics need to be defined. GAP maintains a list of gas injection sources with different gas gravities and impurity

levels (and compositions if compositional tracking is enabled). These can be edited by selecting Options | Injection fluids . When a new file is created, a default entry is supplied with a specific gravity of 0.7 and no impurities. This entry can be edited or a new entry created.

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When gas lifteed well models are set up, the gas source can be set to any gas PVT type defined under Injection fluids. The default gas fluid properties shall be used.

2.4.3

STEP 2 : System schematics

The schematics of the gas injection network shall be defined in this section The various network element models will be entered once the network is in place.

2.4.3.1

Adding Wells

To create the wells, click on the ‘Add Well’ icon, from the toolbar. One may now click on anywhere on the screen and a well icon will be created at that point. Whenever an equipment icon is created, a label can be entered. Click OK once the well name is entered. The first well will be labelled GL1 and the second well GL2. Users are encouraged to use actual well names as labels for their wells. A well (or any equipment type) can be moved across the main GAP interface by holding down the shift key, selecting the icon and moving it to the desired location. Alternatively, select the Move tool from the toolbar and drag the item to the new location. A well (or any equipment type) can be deleted by clicking on the Delete button on the


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toolbar and clicking on the element that needs to be deleted. If a piece of equipment needs to be removed from the system temporarily, then it is preferable to Mask the item – select the Mask tool from the toolbar to achieve this. The option of viewing a grid can be activated by View | Draw Grid.

See the GAP manual for more details on user interface functionality. Ü

TIP: Equipment buttons (such as ‘Add Well’) can be

selected by clicking the right-hand mouse button in the window area to create a drop-down menu. Alternatively, the tools are also selectable from the toolbar buttons.

2.4.3.2

Tie-backs

Joints are needed to hook up the wells to the tiebacks. Joints (or manifolds) are used as connection tools in GAP. They are also used to specify wellheads. To create a joint icon, select the ‘Add Joint’ option from the toolbar. Click on the screen at desired location (above each well icon, for instance). The joint to be connected to the well GL1 will be labelled WH1-GL1, and the second joint will be labelled WH2-GL2. A third joint called "Manifold" shall be used to gather production from the individual

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tiebacks and wells. This will be labelled ‘Manifold’. A fourth joint will be used to indicate the "Riser top". These joints will be connected together with pipes at a later stage.

2.4.3.3

The Platform

The platform is represented as a separator. To create a separator icon, select the ‘Add Separator’ option from the tool bar. Click on the required location on the screen and an icon will be created, as above. The separator will be labelled ‘Platform’.

2.4.3.4

Pipes/Links Ü

Pipes are created using the ‘Add Link’ tool from the TIP: toolbar. The reason for this name is that this tool can also be used to create logical connections (for example, well to reservoir, or compressor to manifold): whether a pipe or a connection is made depends on the equipment being connected.

To connect the different equipment, the ‘Add Link’ button is selected from the toolbar. Connections in integrated models in GAP are made in the direction of fluid © 1990-2009 Petroleum Experts Limited

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flow. Link well GL1 to its wellhead WH1-GL1 by clicking on the well icon GL1, and drag a connection to the WH1-GL1 joint. Repeat the process with GL2 and WH2-GL2. Repeat the process between WH1-GL1 and Manifold and between WH2-GL2 and Manifold. Link the Manifold to the Riser Top: this will become the Riser . Finally, link the Riser top to the Platform.

Ü

It can be seen that pipelines are defined between the wells and the manifold, and the manifold and the riser top. However connections between the wells and the wellhead joints and that between Riser top and Platform only have links between them. This is because the well model is expected to include all equipment up to the well head and account for their pressure drops. Pressure drops are modelled for all other pipes and depend on a pipeline description, as described below.

Labeling

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The tieback between WH1-GL1 and the manifold will be labeled ‘Tie One’. The tieback between WH2-GL2 and the manifold will be labeled ‘Tie Two’. the pipe between manifold and riser will be labelled 'Riser'. Pipe labelling can be achieved by double-clicking on the pipe and entering its label at the top left hand corner of the summary interface.

2.4.3.5

Other Drawing Options

The user interface can be configured in several ways.

· It may be desired to input a name for the model. This is done by clicking on

· ·

Options | Edit System Summary and inputing the title ‘Tutorial GAP Example’ (for example). This text will now appear as a heading for the system network on the main interface. Clicking the right hand mouse button on the main interface and selecting the Fonts option can change the screen fonts. Clicking the right hand mouse button on the title can change the title font. Selecting Icon Sizes from the same drop-down menu can change the sizes of the icons on the GAP screen. This may be useful if building a large model.


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Please consult the user manual or online help for more options.

The basic schematic is now set up, as shown above. The next step is to provide information/models about the various equipment in the network.

2.4.4

STEP 3 : Describing the wells

This section describes set up of the GAP well models. It is recommended that the system is described from the wells to the top node. There are various quality checking functions that can be performed at the well level prior to building the whole system. These will be demonstrated in the following chapters. Ü

TIP (n o te o n en ter in g eq u ip m en t d at a): The basic

means of entering data is from the equipment data entry screen. This can be accessed by double clicking on any equipment icon. The data entry screen consists of a data entry area and a list of network equipment on the right. Descriptions of several pieces of equipment can be entered in one edit session by clicking on the entries in the equipment list to bring up different entry screens.

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Well models

Well GL1 To describe the well model, double click on the Well GL1 icon. This calls up the ‘Well Data Entry - Summary screen’ for this well. Enter the following data:

· · · · · · ·

Label: GL1 Mask: Include In System Well Type: Oil Producer (Gas Lifted) Well file: C:\Program Files\Petroleum Experts\IPM 7.x\Samples\Worked Examples\Dexterity Examples\GL1.OUT Wells can be modelled using Petroleum Experts ’ PROSPER package, as done in this example. Enter the above PROSPER well file in this field, either typing it directly or using the ‘Browse’ button to invoke a file browser. Model: VLP/IPR intersection Control: Gas Lift Control Mode - C a l c u l a t e d (it is not necessary to include a Min and Max Gas Injection Rate )

Click Ok to complete this step, or go directly to the next well using the equipment list on the right. Well GL2


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Enter the following data:· Label: GL2 · Mask: Include In System · Well Type: Oil Producer(Gas Lifted) · Well file: C:\Program Files\Petroleum Experts\IPM 7.x\Samples\Worked Examples\Dexterity Examples\GL2.OUT · Model: VLP/IPR intersection · Control: Gas Lift Control Mode - C a l c u l a t e d (it is not necessary to include a Min and Max Gas Injection Rate ) Click Ok to complete this step. Ü

Note: All data specified above was input on the

summary screen. The data entry screen is divided into three parts as indicated from the toggle buttons at the bottom right of the screen: Summary , Input , and Results. Click on the input and results buttons and have a look at the various categories of data that are available: for example, the first tab on the input screen allows you to set up the gas lift injection source for the well.

2.4.4.2

Generating IPRs From Existing PROSPER Well Models

With a PROSPER file associated to the GAP well model, an IPR import from prosper can be made. When IPR's are transferred, GAP receives three points that lie on the PROSPER IPR along with PVT parameters and reservoir pressure. GAP then performs a match to this data to obtain the PI. To transfer the well IPRs from the existing PROSPER well models select Generate | Generate well IPRs with PROSPER on the GAP main menu and then follow the onscreen instructions. The following screen will be displayed:

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Click on All to select all the wells. The screen as below will show the selected wells. Click on Generate. This will launch PROSPER and import IPR information into GAP.

The IPR generation process begins and the IPRs are transferred in batch mode. No user intervention is required.


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Click OK to go back to the main screen. Double-click on the Well icon to bring up the well summary screen. Note that IPR tab is green indicating that IPR is now valid. Save the GAP file by clicking on save icon Example.gap ’. Ü

. Save the file as ‘ Tutorial Gas Lift

No te: IPR parameters can be entered by hand and

matched from the IPR input screen. From the well data entry screen, select the input button and navigate to the IPR tab. As can be seen, this has been filled automatically during the IPR generation process.

2.4.4.3

Importing Existing Vertical Lift tables to the Well Models

A well is basically defined by an inflow and an outflow; the inflows (IPRs) have been already transferred to the wells in the above procedure. To import/assign the VLP to the well GL1, double-click on the GL1 well icon, click on the VLP tab (should be red if not valid) and browse for VLP file located in C:\ Program Files \ Petroleum Experts \ IPM 7.x \ Samples \ Worked Examples \ Dexterity examples \ GAP\ GL1.VLP. Note that clicking on the VLP tab on the summary screen is equivalent to selecting the Input button followed by the VLP tab.

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Repeat this process for the second well. Its VLP file is located in: C:\ Program Files \ Petroleum Experts \ IPM 7.x \ Samples \ Worked Examples \ Dexterity examples \ GAP\ GL2.VLP Lift curves can be plotted or inspected by clicking on the Plot buttons of the VLP screen. Click on Ok to complete this step. Ü

N ot e: For this exercise, pre-calculated VLP files are

being assigned to the lift curve entries of the wells. If the files have not been prepared, they can be generated in batch mode from GAP using the same approach as was done for batch generation of IPRs. With a PROSPER file assigned to a well, lift curves can be generated by selecting Generate | Generate well VLPs with PROSPER. Alternatively, GAP can import . TPD files (generated by PROSPER) to make .VLP files. To do this, click on Import on the VLP screen and select the required import file.


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STEP 4 : Describing the Pipeline network

True vertical depths (TVDs) of the pipelines shall be input with respect to the platform in this section. The platform is defined to be at zero ft TVD such that the manifold and tiebacks are at 500ft TVD.

2.4.5.1

Riser Description

To describe the riser, double click on the pipeline and this leads to the ‘Pipe Data Entry - Summary Screen’. Enter the following data:

·

Correlation: Petroleum Experts 4

Go to the input section (by clicking on the ‘Input’ button) and enter the following information:

·

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Environment: This can be used to set up special pipe environmental quantities such as ambient temperature or heat capacities for pipeline temperature calculations. The default entries are suitable for our requirements. Leave all

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parameters at their default values. Next, physical description of the pipeline is input. Go to the ‘Description’ tab and enter the following information:

· Enter 0 ft for the downstream TVD (Platform) · Point the cursor to the first cell in the second row in the ‘Segment Type’ · · · ·

Ü

column and select ‘Line pipe’: Length: 500 ft TVD: 500 ft ID: 10" Roughness: 0.0006" (default)

TIP: If measured data for the pipe is available

(rates, pressures e.t.c), a pressure drop correlation can be tuned to reproduce the data. To do this, click on the Match button on the pipe input interface and follow the instructions detailed in the on-line help or the user manual for pipeline matching. Ü

T IP : If no pipeline data is input, then the pipe is

treated as a simple connection between two nodes,


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and zero pressure drop will be modeled across it. GAP does not insist that pipe data is provided. Click Ok to complete this, or navigate to the next pipe. 2.4.5.2

'Tie One' Pipeline description

The above process detailed for the riser is repeated for the other system pipes. · Correlation: Petroleum Experts 4 · Environment: default The pipeline description is:

· Enter 500 ft for the downstream end (Manifold) · Select ‘Line pipe’ in the first cell in the second row in the ‘Segment Type’ · · · ·

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column. Length: 1500 ft TVD: 500 ft ID: 5" Roughness: 0.0006" (default)

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‘TieTwo’ Pipeline description

· ·

Correlation: Petroleum Experts 4 Environment: default

The pipeline description is:

· · · · · ·

Enter 500 ft for the downstream end (Manifold) Select ‘Line Pipe’ in the first cell in the second row in the ‘Segment Type’ column. Length: 1500 ft TVD: 500 ft ID: 5" Roughness: 0.0006" (default)

Click Ok to complete this.

2.4.6

STEP 5 : Calculate Production given total lift gas available

The optimum production from the system given a total amount to gas lift gas available for the system is calculated in this step. GAP determines the optimum © 1990-2009 Petroleum Experts Limited

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amount of gas to be injected in each well to maximise recovery. In order to perform the optimisation, click on | Solve Network and then enter different amount of gas lift gas available given in the following table. Gas available (MMscf/d) 0 3 6 10 20

Click on | Next and production shall be determined for a platform pressure of 250psig.

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Click on Next | Calculate . Make sure that the O p t i m i s e w i t h a l l Co n s t r a i n t s check box is ticked before the calculation is started. GAP will allocate the available gas to the wells to maximise the oil production since gas lift control on each well is set to 'calculated'. When the calculation is finished, click Main to go back to the main screen.


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STEP 6 : Results analysis

To see the effect of the optimised injection of increasing amount of lift gas, click on Results | Detailed | All Separators and Injection Manifolds and the interface below is seen.

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The natural flow production of this production network system is about 4000 BOPD. With 6 MMscf/day of gas injection, an optimal allocation would increase the production to around 4794 BOPD. We also see from these results that increasing the total gas injection beyond 10 MMscf/day does not increase the amount of production by a significant margin. The maximum production available from this system is nearly 5000 BOPD. A plot of oil production against lift gas injection can be displayed by clicking on Plot.


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The optimal gas lift distribution between the wells can be viewed by clicking on Results | Summary | All Wells . Select G as L i f t In j e c ti o n R at e to display how the amount of gas injection to each well varies with total amount available. Click on Plot for a graphical view. Select the following as variables:

· ·

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Gas available: 10 MMscft/d Y axis variable: Oil Rate

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Ü

can view view and and plot plot allo alloca cati tion on resu result lts s for for any any TIP: One can node in the system system by entering entering its data data entry screen in the the usual ual man manner and the then clic lickin king on the Resul sults butt button on.. The The firs firstt tab tab disp displa lays ys the the Allo Alloca cati tion on resu result lts. s. Press Plot to obtain a plot of these results.

This completes the section on building and optimising a network of Gas Lifted wells. Save the file as Tutorial Gas Lift example.gap.

2.5 2.5

Asso Associ ciat ated ed Wate Waterr / Gas Gas Inje Inject ctio ion n Mod Model el Exam Exampl ple e In this section a water injection model will be linked to the previously built gas lifted oil prodcution model. A materal balance prediction will be run on the production model with its associated injection model.

2.5.1

Objectives

The system to be modeled is described below: integrated water injection system comprising of tank model, injection well, a · An integrated feed pipeline and an injection manifold Vertical water injector, injector, tubing tubing down to 5500ft 5500ft (3.5-in (3.5-in I.D.), casing casing down down to 5630ft 5630ft · Vertical (6-in I.D.) IPM Tutorials

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· Reservoir pressure = 4000psi · Injectivity Index = 6stb/day/psi · 500ft riser (ID 6in) down to the injection well The objectives objectives of the exercise exercise is to design design an associa associated ted water injectio injection n system system in GAP which will be coupled to a GAP production system. 2.5.1.1

Learning topics


· Design a simple integrated water injection model in GAP · Associate valid well well models in GAP reservoir/tank models models in GAP · Associate valid reservoir/tank · Calculate system injection potential · Associate/Link Associate/Link the injection injection model to a production production model model in · Perform a performance prediction with both models. 2.5.1.2

GAP

Executive summary


· · · · · · · · · · · 2.5. 2.5.2 2

Couple MBAL tank model to the GAP gas lift production model. Create a GAP water injection model and draw system schematics. Associate an MBAL tank model to water injection model. Design the injection well model in PROSPER. Design the pipeline network. Generating the inflow performance from well model. Generating lift curves for the well. Calculate injection capacity of the system. Save the injection model and couple to production model. Perform prediction run Analyse results. results.

STEP STEP 1 : Set Set the the Prod Produc ucti tion on Mode Modell

The gas gas lifte lifted d produ producti ction on model model previo previous usly ly create created d will will be couple coupled d to MBAL tank models for a material balance balance prediction. This requires adding a Tank Element from the tool bar and defining a reservoir from which the wells are producing. The procedure procedure to couple couple an MBAL tank model has been been describ described ed in the first GAP integrated model dexterity example developed in the tutorial. The MBAL tank model for this example has been designed and can be found in the foll follow owin ing g loca locati tion on:: C:\ C:\ Prog Progra ram m File Files s \ Petr Petrol oleu eum m Expe Expert rts s \ IPM IPM 7.x 7.x \ Samp Sample les s \ Worked Examples \ Dexterity examples \ GAP\ TUTORIAL GAP EXAMPLE_TANK. mbi © 1990-2009 Petroleum Experts Limited

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The The tank tank need needs s to be desc descri ribe bed d in the the prod produc ucti tion on mode model. l. On the the tank tank summ summar ary y screen select Browse and locate the MBAL file (TUTORIAL GAP EXAMPLE_TANK. MBI).

The MBAL model becomes valid. The GAP wells become invalid invalid (red circles). circles). DoubleDouble-clic click k on well model model GL1 to see where the invalid data location is:

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It can be seen that the fractional flow model under IPR | More tab is invalid. Set the relative permeability option to F ro m T an k M o d e l as shown above to revalidate the well models. For more information on fractional flow and relative permeability please review the MBAL User Guide. In order to be able to run a material balance prediction, the model must be made predictive. Ensure that the option to perform predictions in GAP is made active by selecting O p t i o n s | M e t h o d and set P r e d i c t i o n to On


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Using File | Save As, save the file as Tutorial Gas Lift example.gap in a suitable directory.

2.5.3

STEP 2 : Create the Water Injection Model

The water injection model shall be designed in a separate gap file and coupled to the production model later. Ensure that the gap production model is saved. Go to File | New to create a new GAP file. A water injection model is specified in GAP under Options | Method | System type | Water Injection. The model is also made predictive by setting prediction 'On'. Click OK to validate the data.

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The next step is to input the elements constituting the model : reservoir, water injection wells, injection lines and injection manifold. On the main GAP interface, click on the Add tank icon Using the Add well icon

and add a tank.

, add a well.

Using the Add separator/injection manifold icon , add a water injection manifold (a injection temperature must be entered on the Input | Fluid Screen of the manifold). Using the Add joint icon and the well.

, add two joints in between the water injection manifold

Using the Add pipe/link icon , link all the elements together. The elements are linked in the direction of fluid flow starting from the injection manifold to the reservoir/ tank. The network described is shown below.


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Using File | Save As, save the file as WaterInj. GAP in a suitable directory. The physical properties of the different elements constituting the system shall now be specified. The procedure has been explained in detail for each element when the production network was created. The injection system should be completed using the same work-flow/ approach. Design parameters are:

· · · · · ·

Vertical water injector, tubing down to 5500ft, casing down to 5630ft. Geothermal gradient: 50degF at 0feet and 182degF at 5630ft. Surface injection temperature of 70degF and injection pressure 1500psig Reservoir pressure = 4000psi Injectivity index = 6stb/day/psi 500ft riser (ID 6in) down to the injection well

Water shall be injected into the same tank in the production model. Select Browse to locate the MBAL file (TUTORIAL GAP EXAMPLE_TANK.MBI). The water injection well is created using the same procedure described for the production wells. IPR and VLPs must be generated as for any other type of well. Generate VLP for a suitable range of liquid rates, manifold pressure and flowing well head temperatures as may be encountered by the water injection well during a IPM Tutorials

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prediction run. The injection flow line can be completed by using pipe data above for pipe length, pipe inside diameter. Set the well as 'controllable' i.e. wellhead choke can be controlled by the optimiser. This is done either by right clicking on the well, or by selecting dP control as 'calculated on the well summary screen| Input data section.

The red circles around the tank and the well are not present anymore, confirming the validity of the data input on each element of the system. Save the file.

2.5.4

STEP 3 : Link the Production and the Injection System

With the injection model built, the next step is to link the production model and the water injection model. To do so, open the GAP production model. Go to Options | Method and tick the box © 1990-2009 Petroleum Experts Limited

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corresponding to Associated Injection Models | Water Injection . The browsing box will then be available. Browse to the water injection model just built. The path corresponding to this file will appear.

Click OK. Both the production and injection models now appear in the GAP main window. Both models can be visualised side by side in the main GAP window by selecting Window | Tile Vertically.

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It is now possible to make modifications on each model in the same GAP session. Save the project done so far. Click on File| Save as and each model will be saved separately as shown by the following screen. Click Continue to save the production and water injection models in the same directories chosen previously. If this is not the case, simply alter the file path name on the interface.


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STEP 4 : Performing the Material Balance Prediction

A material balance prediction can now be run. Using the Run Prediction icon , start the material balance prediction process. The first screen enables one to select the prediction start and end dates as well as the step size.

Several options are available for water injection control (and/or gas injection). - Tank target pressure: This option maintains the reservoir pressure at specified value by voidage replacement with water. - Voidage replacement: Water injection by voidage replacement, as specified by a percentage input by the user. - Water recycling : this option enables to inject a defined percentage of the produced water - Fixed Rate : this option enables to inject a defined rate of water. These constraints will be honoured if selected because the injection well has has a theoretical wellhead choke applied across it (i.e dP choke control). Set a fixed water injection rate of 3000 STB / d.

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Click Next to go to the next prediction screen : It summarises the input data for the tank chosen.

Select Next and input 3MMscf/day as gas lift gas available.


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Select Next and input a separator pressure of 250 psig.

Select Next and input an injection manifold pressure of 2000 psig.

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NOTE: The water injection well VLP data set must have ben generated with M a n i f o l d P r e s s u r e range that includes the 2000 psig.

Select Optimise with all Constraints and Calculate. This allows the Solve Network cycle to be performed for each of the 16 time steps requested, while respecting the constraints input.


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GAP reports the limiting constraints in the system. In this case, these are the

maximum gas lift gas available and the fixed water injection rate. Once the calculation is finished, select Main and return to the main GAP window. To inspect the results, double click on the tank and select Results | Show MBAL Results. This enables accessing the global prediction results for the tank. To check that the constraint on the water injection rate as been respected, select Plot | Variables and choose the variables you want to display on the plot, Average Water Injection Rate Vs. Time .

Select Done and the plot is displayed. It is then noticeable that the constraints on the water injection rate set previously as been fulfilled. The scales can be set by Scales | Edit.

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Associated Gas Injection Model

A similar procedure can be followed to set up a GAP surface network model associated with a Gas Injection System, as shown on the following screenshots.


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Chapter

3

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Physics Examples This section contains the following tutorials:-

· PROSPER Gas Lift Example: This example focuses on the design of a gas lifted oil well in PROSPER.

· PROSPER ESP Example: This example focuses on the design of a ESP (Electrical submersible pump) lifted oil well in PROSPER.

· MBAL Gas History Matching Example: This example is a continuation of the MBAL gas example outlined in the dexterity section. It focuses on matching the model to production history and preparing the model for a prediction through fractional flow matching.

· MBAL Oil History Matching Example: This example focuses on the design of an MBAL oil reservoir model and shows how to history match the model to production data. All the example files can be found under: C:\Program Files\Petroleum Experts\IPM 7.x\Worked Examples\Physics Examples

3.1

PROSPER Gas Lift Example Gas lifting a well involves the injection of gas into the well to reduce the mixture density of the fluid column (i.e. lighten the fluid), reduce the gravity pressure drop in the well and this increases inflow into the well (due to a reduce flowing bottom hole pressure). This example assumes that the user is already familiar with setting up well models in PROSPER. All the example files can be found under: C:\Program Files\Petroleum Experts\IPM 7.x\Samples\Worked examples\Physics Examples\Gas Lift

3.1.1

Objectives

The objectives of the exercise are: 1. Design a naturally flowing well in PROSPER. 2. Quality check the test / production data that is available. The well test data IPM Tutorials

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quality check is based on physics providing some validity of test measurements. 3. Based on the checked data, the PVT and flow models (VLP+IPR) are input. 4. Design a new gas lift system for this well. 5. Use PROSPER QuickLook analysis for performance diagnosis. Data Available: PVT Data: · Temperature = 250.0 deg F · Bubble Point Pb = 2200.0 psig · GOR at Pb = 500 scf/stb · Oil FVF at Pb = 1.32 rb/stb · Oil viscosity at Pb= 0.4 cp · Oil gravity = 39.0 API · Gas gravity = 0.798 · Water Salinity = 100,000 ppm Gradient Data:

Data Set 1

· · · · · · ·

Well head pressure = 264.0 psig Water cut = 20.3 % Liquid rate = 6161.0 stb/day GOR = 432 scf/stb Gas Lift = 0 MMscf/day Injection depth = 13000 ft Pressure @ 14800 ft = 3382.0 psig

Data Set 2 · Well head pressure = 264.0 psig · Water cut = 20.3 % · Liquid rate = 1100.0 stb/day · GOR = 500 scf/stb · Gas Lift = 1.0 MMscf/day · Injection depth = 8000.0 ft · Pressure @ 1500 ft = 500.0 psig 3.1.1.1

Learning topics


· · · ·

Design a naturally flowing well in PROSPER Perform data quality check Model validation Design of a gas lifted well in PROSPER


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The single well model will be designed one step at a time and at each step any available test / production data available will be used to validate the model. As new test data becomes available, it will be checked with the model and any inconsistency will be investigated from an engineering and physics point of view.

3.1.1.2

Executive summary


· · · · · · · 3.1.2

Define modeling objective in PROSPER Input PVT model and match BO correlations to PVT laboratory data Input equipment data: deviation survery, equipment, geothermal gradient Input IPR model. Quality check/Validate test data with PVT using quality control flow correlations Perform a new gas lift design PROSPER Validate gas lift well model using Quicklook tool in PROSPER

STEP 1 : Model Setup

The type of well being modelled shall be defined under System Options. Start from a new prosper file. Select the Options | Options menu in PROSPER and select the following: Fluid Method Separator Emulsions Hydrates Water viscosity Flow type Well type Artificial lift method Type Predict Model Range Output Well completion type Gravel pack Inflow type Gas coning

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Oil and water Black oil Single-stage No Disable warning Use default correlation Tubing flow Producer Gas lift (Continuous) No friction loss in annulus Pressure and temperature (offshore) Rough approximation Full system Show calculating data Cased hole No Single branch No

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Next a Black Oil fluid PVT model shall be input (The Black oil method was selected for fluid PVT description under system options). Black oil correlations shall be matched to laboratory data and the most suitable Black oil correlation which reproduces fluid PVT behaviour will be selected. Select | PVT | Input Data and enter the following fluid properties at standard conditions: Solution GOR Oil gravity Gas gravity Water salinity (No gas impurities)

500 scf/stb 39 API 0.798 100000 ppm


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Click the Match Data button on the above dialog and enter the PVT match data available at bubble point conditions of the fluid. Temperature 250 degree F Bubble point 2200 psig GOR @ bubble point 500 scf/stb Oil FVF @ bubble point 1.32 rb/stb Oil viscosity @ bubble point 0.4 cp

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Click Done on the above dialog to go back to the PVT input dialog. Conduct the matching procedure by clicking the Regression button and then the Match All button.

Once the correlations have been matched to data, click the Parameters button to view the statistics and select the best correlation that closely reproduces PVT behaviour. Based on the regression parameters (parameter 1, a multiplier and parameter 2, a shift factor) and standard deviation, select the best model. Ideally the standard deviation should be very small, parameter 1 should equal 1 and parameter 2 should equal zero.


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From the regression results, the Glaso correlation for Pb, Rs and Bo and Beggs et al correlation for oil viscosity give the best match and are selected for the PVT model. Click on | Done | Done to go back to the main PVT screen. Select the correlations to use in the main PVT screen.

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Once this is done, click on Done to return to the main window. Next step is to define the well configuration./ equipment data. Click on System | Equipment (Tubing etc.) menu option and input the following equipment data: Deviation Survey The deviation survey is:

Measured depth (ft)

True vertical depth (ft)

0

0

1000

1000

2500

2405

6500

5322

15200

11500


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Down hole Equipment

Type

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Measured depth Internal diameter (ft) (in)

Roughness (in)

X’mass tree

0

Tubing

14500

3.96

0.0006

Casing

15200

6.00

0.0006

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Geothermal Gradient The formation geothermal gradient is given below:

Measured depth (ft)

Formation temperature (degree F)

0

50

15200

250

Overall heat transfer coefficient (OHTC):8 BTU/hr/ft2/F


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The next step is to define an Inflow performance relationship. Click on System | Inflow Performance and select the Darcy analytical IPR model. Input the parameters given below: Reservoir model Mechanical / Geometrical skin Reservoir pressure Reservoir temperature Water cut Total GOR Relative permeability

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Darcy Enter by hand 3844 psig 250 degree F 20.3 % 500 No

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Click on Input data to enter the reservoir properties. Reservoir Permeability Reservoir thickness Drainage area Dietz shape factor Well bore radius

100 md 100 ft 100 acres 31.6 0.354 ft


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Click on the tab labelled ‘Mech/Geom Skin’ and input a skin value of zero i.e. no feature in reservoir causes an additional pressure drop

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Next, the IPR is calculated to register the Absolute Open flow potential (AOF) of the reservoir. Click on the Calculate button to get the following IPR plot:


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Click on Main on the IPR plot menu to go back to the main PROSPER window. The next step is to define gas lift data: gas properties, injection depths and pressures e.t.c. Click on System | Gaslift Data menu and enter the gas lift data as follows. Gaslift gas gravity Mole percent H2S Mole percent H2S Mole percent H2S GLR injected Gas lift method Maximum Depth of injection Casing pressure DP across valve

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0.7 0% 0% 0% 0 scf/stb Optimum Depth of injection 13000 ft 1900 psig 100 psi

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As the gas lift data suggests, an optimum depth of injection has been chosen but the injection depth is limited to 13000 feet (the packer depth). Thus with a casing pressure of 1900psi and 100psi pressure loss across valve, prosper will determine the optimum point of injection that corresponds to maximum liquid produced. The 0.7gravity gas will be injected at this depth depending on gas injection rates or GLR injected specified. Various values of injection rates or GLR injected can be sentisized on during a system calculation. Click on Done to complete this and to go back to the main PROSPER screen. Save the file using File | Save As as GLIFTG.OUT for a directory of choice.

3.1.3

STEP 2 : Well Model Validation and Data Quality Check

In this section, the response of the model shall be compared to measured data. The first step is to perform a data quality check. Data set 1 shall be sued for model validation. To match model to test data, Select Matching | Correlation Comparison | Tubing from the main PROSPER menu and enter the following data and selecting the vertical lift correlations as shown below: Well head pressure Water cut Liquid rate GOR GOR free Gas Lift gas rate

264.0 psig 20.3 % 6161.0 stb/day 432 scf/stb 0 scf/stb 0 MMscf/day


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Injection depth Pressure @ 14800 ft Correlations

13000. ft 3382.0 psig Duns and Ros Modified Hagedorn Brown Fancher Brown Petroleum Experts 2 Petroleum Experts 3

Click on Calculate | Calculate to perform the calculations. Plot to view the results.

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It can be seen at the bottom right hand corner of the plot that the test data point lies to the left of the pressure traverse generated by the Fancher Brown correlation. The Fancher Brown correlation is a non-slip correlation i.e. it assumes equal flow velocities for liquid and gas. It thus predicts a no-slip holdup and a minimum pressure drop. In reality however, there is always some slip between liquid and gas, holdup is increased and the pressure drop in the pipe is increased. However, the plot indicates that actual pressure at a point in the well (test point) is lower than the Fancher Brown correlation which is not physically possible. This suggests some inconsistent data in the PVT model and/or test data provided equipment data description of the well is accurate. From a review of the test data, a GOR of 432 scf/stb at a reservoir pressure of 3844psi was input. However the PVT model shows that the solution GOR at bubble point pressure is 500 scf/stb. If the PVT model is assumed accurate, then the test data input is inconsistent with this and should be reviewed. The test GOR is changed to 500 scf/stb and the calculation is re-done.


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The following plot is obtained:

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It can be seen that with consistency between the test data and PVT model, the test data data point point plots plots to the right right of the Fanch Fancher er Brow Brown n correl correlati ation on.. This This illus illustra trate tes s the quality check procedure. The next step involves matching a vertical lift correlation to the test data to reproduc reproduce e actual actual pressure pressure drops in the well. The matched matched correlation correlation shall be used used in the analysis. Well test Data set 2 shall be used for this purpose. Again, going through the correlation correlation comparison comparison steps as done for Data set 1, the data data shal shalll be qual qualit ity y chec checke ked d by perf perfor ormi ming ng pres pressu sure re grad gradie ient nt calc calcul ulat atio ions ns with with different vertical flow correlations. Data Set 2 · Well head pressure = 264.0 psig · Water cut = 20.3 % · Liquid rate = 1100.0 stb/day · GOR = 500 scf/stb · Gas Lift = 1.0 MMscf/day · Injection depth = 8000.0 ft · Pressure @ 1500 ft = 500.0 psig

Performing the calculations and plotting the results, the following plot is obtained:

The test data point lies to the right of the Duns and Ross Modified (DRM) correlation. correlation. © 1990-2009 Petroleum Experts Limited

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In like manner as the Fancher Brown (FB) correlation , the DRM correlation represents the maximum pressure loss obtainable in a well if the flow regime is slug flow. One can verify that the flow regime at the gauge depth (i.e. test point) is slug flow flow by chec checkin king g the the gradie gradient nt result results s as shown shown below below.. This This indica indicates tes incon inconsis sisten tentt data between the PVT and test measurements assuming well configuration as input under equipment data is accurate.

It can be further noticed that for the same well head pressure and IPR, the gas lift well test (Data set 2) produces at lower flow rates than at naturally flowing conditions (Data set 1). This indicates some inconsistency. If PVT model is assumed accurate, then the well test data needs to be reviewed. The other point to note is that for the same well head pressure and IPR, with gas lift we are getting lower flow rates than without gas lift as indicated by data point one. It coul could d be that that the the data data poin pointt is wrong wrong or the the PVT data are are incor incorrec rect. t. Howe However ver we already know that our PVT data data are correct, so the data point must be incorrect. Since Data set 1 has been quality checked, the VLP correlations can be matched to it. The matching process seeks to tune the correlations to reproduce the test data point point by matchin matching g the two main pressure pressure drop componen components ts i.e. gravity gravity and friction friction using multipliers (parameter (parameter 1 and parameter 2) for each correlation. The correlation IPM Tutorials

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that best matches the test will be selected to model flow in the tubing. Select Matching Matching | Matching Matching | IPR/VLP IPR/VLP (Quality Check) and input test data point 1 in the VLP/IPR matching interface as shown below: Well head pressure Tub Tubing head tem temper perature ture Water cut Liquid rate GOR GOR free Gas Lift gas rate Injection depth Pressure @ 14800 ft

264.0 psig 132.8 degree ree F 20.3 % 6161.0 stb/day 500 scf/stb 0 scf/stb 0 MMscf/day 13000. ft 3382.0 psig

Sele Select ct the the matc match h data data spre spread adsh shee eett row row numb number er and and clic click k the the E s ti t i m at a t e U V al al u e butt button on.. This This proc proced edur ure e vali valida date tes s the the temp temper erat atur ure e mode modell in PROSPER by back calc calcul ulat atin ing g the the righ rightt Ov Over eral alll Heat Heat tran transf sfer er co-e co-eff ffic icie ient nt (OHT (OHTC C or U-va U-valu lue) e) whic which h reproduces the actual temperature profile across the well using the Rough approxim approximatio ation n tempera temperature ture model. Once this is calculat calculated, ed, it should should be updated updated in t h e r m a l G r ad ad i en e n t section of the downhole equipment data. Select Yes on the G e o th the pop up menu to update the U-value.


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Sinc Since e a corr correl elat atio ion n comp compar aris ison on has has been been cond conduc ucte ted d on the the data data,, Hage Hagedo dorn rn and and Brown, Brown, PE2 and PE3 correlat correlations ions were closest closest to the test point. point. The next step is to match these VLP to the measured data and the best correlation will be selected. Click the Match VLP button and select the following correlations:

· Hagerdorn Brown 2 · Petroleum Experts 2 3 · Petroleum Experts 3

With the match calculations performed, the match parameters (Parameters 1 and 2) can be accessed by clicking on Statistics.

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Petroleum Experts 3 correlation gives the best match and will be selected as the vertical

lift correlation for the well. With the VLP correlation matched to test data, the next step is to validate/match the IPR model. Since the VLP reproduces the actual pressure drop in the well (i.e passing through the test point); it can be extrapolated to the bottom of the well to obtain the bottom hole pressure at the test conditions (Qliq, WC and GOR). The flowing bottom hole pressure and Qliq will plot as a point on a VLP/IPR plot. The matched VLP honours this point and from the concept of nodal analysis, the IPR model can be tuned (depending on parameters of most uncertainty in the IPR model) to pass through this test point; hence honouring the measured data. This is achieved in the VLP/IPR matching section. From the correlation matched parameters screen, click on | Done | Done. This leads to the VLP/IPR matching interface. Select ‘ VLP/IPR’ to perform the IPR match. © 1990-2009 Petroleum Experts Limited

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The objective of this calculation is to obtain the flowing bottom hole pressure for the test conditions using the matched VLP correlation. Using the matched PE3 correlation, click on Calculate . The results of the calculation and estimated flowing bottom hole pressure are indicated.

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It can be seen that the S o l u t io n R at e and flowing/solution bottom hole pressure (BHP) as obtained from the model do not correspond with the T es t R a te and Test BHP. Select P l o t and zoom using a left-click and mouse drag over the test point to observe the VLP / IPR match.


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The square box is the test point which corresponds to test rate and test BHP as estimated form the matched VLP correlation. The cross indicates the solution rate and pressure as calculated by the model. For the model to reproduce the measured data, the VLP and IPR should intersect at the test point. Rate and pressure errors are displayed on the right of the plot screen. The IPR model can then be adjusted to minimise the errors. There is no universal rule applicable to IPR adjustment. It is based on the IPR model being used and knowledge of the system. For example, the reservoir pressure and/ or skin may be adjusted to achieve a match. It depends on the users judgement. For this exercise, the reservoir pressure shall be changed. Change the reservoir pressure from the V L P /I PR M a t c h i n g dialogue to 3874psig. Select VLP/IPR and C a lc u l a t e and view the tabular results then P l o t to view the graphical solution. Click on Finish to close the plot window. Select the IP R button and change the reservoir pressure in the IPR main screen to 3874 psig to up-date the IPR pressure.

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This concludes model validation exercise: matching model to test data. Save the file as GliftG1.out in a suitable directory .

3.1.4

STEP 3 : Gas Lift Design

The objective of this section is to design a gas lift for the prosper well model designed previously. The optimum gas lift rate at the desired well head pressure shall be calculated and the gas lift design performed. Also the various design parameters e.g. casing pressures required to open the valves at injection depth and at surface will be calculated. The design shall be performed for the well producing at 50% watercut. Gas available for injection is 6MMscf/day at 1900 psig casing injection pressure. Select the Design | Gas Lift | New Well menu item. Input the following data. Casing sensitive valves which open at casing pressure shall be used. Design rate method Maximum Liquid rate Maximum gas available Maximum gas during unloading Flowing top node pressure Unloading top node pressure

Calculate from max production 20000 stb/day 6 MMscf/day 6 MMscf/day 250 psig 250 psig © 1990-2009 Petroleum Experts Limited

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Operating injection pressure Kick off injection pressure Desired dP across valve Maximum depth of injection Water cut Minimum spacing Static gradient of load fluid Minimum transfer dP Safety for closure of last unloading valve Total GOR Valve type Min CHP decrease per valve Valve settings Dome pressure correlation above 1200 psig Valve spacing Method Check rate conformance with IPR Vertical lift correlation Surface pipe correlation Use IPR for unloading Orifice sizing on Current Valve Type Maximum port size Thornhill-Craver De-rating

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1900 psig 1900 psig 200 psi 13500 ft 50% 500 ft 0.45 psi/ft 25% 0 psi 500 scf/stb Casing sensitive 20 psi All valves Pvo = gas pressure Yes Normal Yes Petroleum Experts 3 Beggs and Brill Yes Calculated dP at orifice Baker | B1 | Type_b 53/64-in 100% (no de-rating applied)

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Once the valve type has been selected, select Continue. The first step in the design is to generate the gas lift performance curve by clicking the Get Rate button. Select the Plot button at the top of the screen and the generated performance curve is as shown:

The performance curve of a gas lift design plots the oil rate produced with increased gas injection rates. As discussed earlier, a well is gas lifted to decrease the pressure loss in the tubing string by decreasing the gravity component of pressure drop. The greater the amount of gas injected; the lighter the fluid column will be. However as the amount of gas injected increases, the other major pressure drop component (friction) also increases. An injection stage is attained when any further increase in gas injection increases the friction pressure loss more than the relative decrease in gravity pressure loss. This causes the observed shape of the gaslift gas perfomance plot. A look at the performance curve shows that at a gas lift rate of 6 MMscf/day the oil production is about 3400 stb/day. From this plot PROSPER determines the gas lift required for maximum oil production. In cases where the Maximum Gas Available value is higher than the Maximum Gas during Unloading , the program will only inject the optimum gas into the well, based on the specified maximum gas during unloading value which in this case is 6 MMscf/day. In cases where the available gas is less than optimum gas, the actual available gas value will be used. The next step is to proceed to the actual gas lift design which shall be conducted with 6MMscf/day (maximum gas lift gas available). Click on Design to do this.


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With the design completed, click on Plot to observe the design in terms of fluid pressure gradients in the tubing and annulus.

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Click on Finish to exit the plot and return to the design interface. Here, a click on Results brings up the calculated gas lift design parameters. Click on Calculate to obtain the dome pressures and test rack opening pressure settings required.

This concludes the gas lift design. For any calculation involving this design, the gas lift parameters (valve depths and injection pressure) needs to be transferred form the design to the gas lift data panel on the PROSPER main interface. To do this, exit the gas lift design section and double click on the gas lift data panel on the main interface. Select valve depths © 1990-2009 Petroleum Experts Limited

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specified and click on "Transfer | From Gas lift design" and the valve depth data will be copied across. Go back to the main screen, and save the file as GliftG2.out in a suitable directory. 3.1.5

STEP 4 : Use of QuickLook Diagnostic tool for gas lift performance validation

Ü

Note: In this section, the Quicklook diagnostic tool for gaslift shall be used to validate a PROSPER gas lift well model against measured data.

To access the Quicklook section, select Matching – QuickLook. It is assumed that measured data is as given below (updated form Data set 1) Tubing head pressure Tubing head temperature Liquid rate Water cut Total gas rate Gas injection rate Casing head pressure

264 psig 160.7 degree F 6161 stb/day 20.3 % 6.555 MMscf/day 4.1 MMscf/day 1750 psig

Input the values under minimum surface measurements.

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To enter the valve data, select the Valves button on the above interface. The following screen appears:

The valve data from the just concluded design can be transferred by selecting Transfer| From Gas Lift Design on the screen below.


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Next click on Done | Calculate | Calculate | OK | Plot to get the following diagnostic plot which shows the pressure traverses along the tubing and annulus of the well.

The QuickLook principle calculates well pressure traverses in two directions: one beginning from the wellhead and going to the sand face, and the other going from the sand-face up to the wellhead. This is done for both tubing and casing to a give four pressure gradients. The downward gradients are based on measured data (THP, liquid flow rates, WC, GOR for tubing gradient; and CHP, gas injection rates for casing gradient), while the upward gradients depend on the inflow (in the case of the tubing pressure) and on the pressure drop across the orifice (as regards the casing pressure). If the model reproduces observed conditions in the well (assuming accurate test measurements), the pressure traverses in both directions should be identical for tubing and annular flow. If this is not the case, likely cause of the deviations need to be investigated. From a review of the plot it can be seen that we see that the tubing traverse IPM Tutorials

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calculated starting from the flowing bottomhole pressure is higher than the measured tubing traverse. This suggests that the inflow potential is too high. The likely cause of this will depend on the IPR model being used and the engineers knowledge of the project. For example, it may be as a result of reservoir pressure and/or skin. For the purposes of this example, it will be assumed that the skin value is incorrect and is 5.5. To change this, exit from the Q uick-Look dialogue and update the IPR skin value. Return to the Quick-Look calculation and recalculate the gradient:

It will be seen that the tubing curves now overlap. The next step is to compare casing pressure traverses above the orifice. The calculated upward casing pressure traverse is now lower compared to the measured casing pressure traverse. This suggests that the pressure drop across the orifice for some reason (like scaling) has increased. In order to match the gradients, a smaller orifice diameter can be chosen. Decrease the orifice diameter to 25/64” and re-perform QuickLook calculations. The plot below is obtained.


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The results show a match between the tubing and annular gradients. This exercise shows how the quick look diagnostic tool can be sued to investigate/troubleshoot performance of gas lifted wells provided reliable flow and pressure measurements are available. Save the file as GliftG3.out in a suitable directory.

3.2

PROSPER ESP Example An ESP (Electrical Submersible Pump) is installed in a well to provide additional energy for the fluid to flow at a target production rate and well head pressure. This example presumes that the user is already familiar with setting up well models in PROSPER. All the example files can be found under: C:\Program Files\Petroleum Experts\IPM 7.x\Samples\Worked Examples\Physics Examples\ESP

3.2.1

Objectives

The objectives of the exercise are:

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1. Design a naturally flowing well in PROSPER. 2. Quality check the test / production data that is available. The well test data quality check is based on physics providing some validity of test measurements. 3. Based on the checked data, the PVT and flow models (VLP+IPR) are input. 4. Design a new ESP lift system for this well. 5. Use PROSPER QuickLook analysis for performance diagnosis. Data Available: PVT Data: · Solution GOR = 392.0 scf/stb · Oil Gravity = 37.66 API · Gas Gravity = 1.045 · Water Salinity = 94334 ppm · Temperature = 205 deg F · Bubble Point Pb = 1361.0 psig

Pressure Psig

GOR scf/stb

Oil FVF rb/stb

1361.0

392

1.289

3215

392

1.25

Oil Viscosity cp 0.66

Gradient Data: Data Set 1 · Well head pressure = 334 psig · Tubing Head Temperature = 174 deg F · Water Cut = 6 % · Liq. Rate = 5200 stb/day · GOR = 392 scf/stb · GOR free = 0 scf/stb · Pressure @ 7677.2 ft = 2329.0 psig 3.2.1.1

Learning topics


· · · · ·

Design a naturally flowing well in PROSPER Perform data quality check Model validation Design of a ESP lifted well in PROSPER

The single well model will be designed in a step by step fashion and at each step any available test / production data available will be used to validate the model.


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3.2.1.2

Executive summary


· · · · · · · 3.2.2

Define modeling objective in PROSPER Input PVT model and match BO correlations to PVT laboratory data Input equipment data: deviation survery, equipment, geothermal gradient Input IPR model. Quality check/Validate test data with PVT using quality control flow correlations Perform a new ESP lift design PROSPER Validate ESP lift well model using Quicklook tool in PROSPER

STEP 1 : Model Setup

The type of well being modelled shall be defined under Systems Options. Run PROSPER and go to the Option menu in PROSPER. Select the following options:

The options selected are:

· The fluid type is oil · PVT behaviour will be modelled as Black oil PVT technique with a single stage · IPM Tutorials

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· Temperature calcuations shall be performed using the rough approximation · · · · ·

temperature model. The fluid flows through the tubing No emulsion forms Presently, the well is naturally flowing - No artificial lift option is selected. Reason for this shall be discussed later. It is a cased hole with no gravel pack. There is no gas coning and the well completion is single branch/lateral.

Next a Black Oil fluid PVT model shall be input (The Black oil method was selected for fluid PVT description under system options). Black oil correlations shall be matched to laboratory data and the most suitable Black oil correlation which reproduces fluid PVT behaviour will be selected. On the main interface, go to the PVT section by selecting PVT | Input Data. Input the PVT data as indicated below.

Input the PVT match data available by clicking the Match Data button on the above screen. This is shown below:


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Click Done on the above dialog to go back to the PVT input dialog. Conduct the matching procedure by clicking on the Regression button and then the Match All button. The program performs a regression analysis on all the entered data with all standard black oil correlations that are available in PROSPER.

To display the regression parameters and standard deviations for all the correlations, click on Parameters .

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Based on the regression parameters (parameter 1, a multiplier and parameter 2; a shift factor) and standard deviation, select the best model. Ideally the standard deviation should be very small, parameter 1 should equal 1.0 and parameter 2 should equal zero. From the regression results, the Standing correlation gives the best match for Pb, Rs and Bo while Beggs correlation gives the best match for oil viscosity. Once this is done, click the Main button to go back to the main window. Ensure the matched correlations are selected on the main PVT interface (see below)


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With the PVT match completed i.e. having a valid fluid PVT model which reproduces fluid behaviour behaviour in reality, reality, the next step is to input input the well configu configurati ration/ on/ equipme equipment nt data. To do this, go to the main interface, select System | Equipment (Tubing etc.) from main menu and input the equipment data as follows: Deviation Survey:

The deviation survey is as follows: Measured depth (ft)

True vertical depth (ft)

0

0

463.3

463.3

2399.9

2368.4

3450.1

3256.6

4649.9

4100.1

5200.1

4467.5

6899.9

5673.9

7450.1

6079.7

8687.7

7280.2

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This survey survey is the referenc reference e for MD - TVD depth convers conversions ions.. The deviation deviation survey survey should start from zero (i.e. a reference depth). Where this zero depth is refernced to is up to the user. user. Howe However ver,, it is impor importan tantt that that all other other depth depth entrie entries s in teh model model should be consistent with this zero depth reference. The next step is to define the equipments in the well itself. No surface data equipment is available. Down-hole equipment:

The following equipment data is available for the well. No tubing Outer Diameter data is input at the moment. The data is input later when the ESP artificial lift option © 1990-2009 Petroleum Experts Limited

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is selected. Type

MD (ft)

Tubing ID (in)

Tubing OD (in)

Casing ID (in)

X’mas tree

59.4

-

-

-

Tubing

689.0

3.96

4.5

8.68

SSSV

-

2.13

-

-

Tubing

7660.8

3.96

4.5

8.68

Restriction

-

2.31

-

-

Tubing

7677.2

3.96

4.5

8.68

Casing

7860.9

-

-

8.68

Casing

8169.3

-

-

6.18

Casing

8687.7

-

-

3.96

All roughness roughness of tubing tubing / casing = 0.0006 0.0006 in

Next Next,, geot geothe herm rmal al grad gradie ient nt and and OHTC OHTC (U-v (U-val alue ue)) are are spec specif ifie ied d as give given n belo below w for for temperature calculations in the well. Geothermal Gradient:

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The formation geothermal gradient is as given below: Measured depth (ft)

Formation temperature (degree F)

59.4

60

8687.7

205

Over Ov eral alll Heat Heat Tra Trans nsfe ferr Coef Coeffi fici cien entt (OHT (OHTC) C)::

3 BTU/ BTU/hr hr/f /ft2 t2/F /F

The Average Heat Capacities are kept at their default values. The next step is to define define an inflow inflow into the the well well from from the reservo reservoir. ir. This involves involves defining an IPR model. Select the System | Inflow Performance menu item to select an IPR model. Input the IPR data as shown in the following dialogs: Reservoir model Reservoir pressure Reservoir temperature Water cut Total GOR Relative permeability

PI Entry 2468 psig 205 degree F 6% 392 No


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The PI IPR model based on test measurements is selected. Click on Input data tab to input a PI of 7.19 stb/day/psi for the system.

Click the Calculate button to view the IPR and the Absolute Open flow potential calculated.

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3.2.3

142

STEP 2 : Well Model Validation and Data Quality Check

In this section, the response of the model shall be compared to measured data. The first step is to perform a data quality check. Data set 1 shall be sued for model validation. For ESP's pressure traverse calculations are performed form the bottom to the top of the well unlike naturally flowing wells where calculations are form top to bottom. However, the bottom hole pressure (which becomes first calculation node) is unknown for an ESP lifted well. But from test data, the well head pressure and gauge pressure above the pump are known. Above the pump, the pressure drop calculations are similar to natural flow conditions but with high bottom hole pressures (pump discharge point). This means a flow correlation in the model can be matched to the test point above the pump and this is why the ESP was not selected for artificial lift initially. After the well section above the pump is matched to test data, the ESP option will be selected. Therefore the first step in model validation is to match a lift correlation to test data above the pump. Select the Matching | Correlation Comparison | Tubing menu item and input the following data, selecting the highlighted correlations.


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Perform the calculations (by clicking the Calculate | Calculate ) and plot the results.

The above plot shows that the test data point lies on the right of the Pressure

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traverse generated by the Duns and Ros Modified (DRM) correlation. The DRM correlation represents the maximum pressure loss obtainable in a well if the flow regime is slug flow. One can verify that the flow regime at the gauge depth (i.e. test point) is slug flow by checking the gradient calculation results on the previous interface. For the well conditions, the plot indicates tubing pressures greater than the DRM correlation. This indicates inconsistency between the PVT model and test data assuming equipment description is accurate. Assuming accurate PVT model for this example, then the test data has to be reviewed. A water cut of 6% was input at test conditions. This is a low value for a naturally flowing well being considered for artificial lift. A re-check of test data now indicates that actual water cut is 34% and not 6%. Changing this value on the Tubing correlation comparison interface and re-calculating the gradients, the following plot is obtained.

It can be seen that the test data point plots to the left of DRM correlation, and this concludes the quality check process. The next step involves matching a vertical lift correlation to the test data. The matching process seeks to tune the correlations to reproduce the test data point by matching the two components of pressure drop i.e. gravity and friction using multipliers (parameter 1 and parameter 2) for each correlation. The correlation that best matches the test will be selected to model flow in the tubing. Select Matching | Matching | IPR/VLP (Quality Check) and input test data 1 on the VLP/IPR matching interface as shown below (note that a 34% water cut value will be used). © 1990-2009 Petroleum Experts Limited

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Perform the correlation match by clicking the M a t c h V L P button. Select the following correlations from the list: Hagedorn Brown Petroleum Experts 2 Petroleum Experts 3 Click the Match button again to calculate the match parameters. Once completed, the match parameters are reviewed by selecting the S t a t i s t i c s button:

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Petroleum Experts 2 gives the best match and will be selected later as the vertical lift

correlation. This concludes model validation and data quality check for the example. Save the file as ESPG.out in a suitable directory . 3.2.4

STEP 3 : ESP Design

The objective of this section is to design an ESP lifted oil well for the previous example. The differential pressure required by the pump to meet the design parameters are calculated and based on this, a pump, motor and cable that can meet this design and fit in the well are selected. The design shall be performed at a target liquid rate of 6000stb/day, 60% water cut against a well head pressure of 100psig. The pump shall be placed at 7660ft and a cable of 7710feet will supply power to the pump via the motor. From the O p t i o n s menu set the A r t i f i c i a l L i f t M et h o d to electrical submersible pump. Go to the D o w n h o l e Eq u i p m e n t Se c t i o n and complete the tubing and casing outer diameter information.


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Type

MD (ft)

Tubing ID (in)

Tubing OD (in)

Casing ID (in)

X’mas tree

59.4

-

-

-

Tubing

689.0

3.96

4.5

8.68

SSSV

-

2.13

-

-

Tubing

7660.8

3.96

4.5

8.68

Restriction

-

2.31

-

-

Tubing

7677.2

3.96

4.5

8.68

Casing

7860.9

-

-

8.68

Casing

8169.3

-

-

6.18

Casing

8687.7

-

-

3.96

On the main menu, select Design | Electrical Submersible Pump . On the ESP Design interface, input the following data. An initial assumption that no gas separation is required at the pump inlet will be taken (i.e. gas separation IPM Tutorials

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efficiency is zero). Pump depth Operating frequency Maximum OD Length of cable Gas separator efficiency Design rate Water cut Total GOR Top node pressure Motor power safety margin Pump wear factor Pipe correlation Tubing correlation

7660 ft 60 Hz 6 in 7710 ft 0% 9000 stb/day 60 % 392 scf/stb 100 psig 0% 0 Beggs and Brill Petroleum Experts 2

Click on Calculate on the above dialog and Calculate again to determine the pump head, fluid power required and other design parameters:


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With the calculations completed, the need for a gas separator at pump inlet can be checked using an empirical correlation (Dunbar plot). Click on Sensitivity and the plot appears. The Dunbar plot is a plot of Intake pressure against gas entering the pump (i.e. GLR at pump intake).

The different lines on the Dunbar plot are for different levels of gas separation efficiency at pump intake. When the test point plots above the Dunbar factor, a gas separator is not necessary at pump inlet (as in this case). If the point plots below the Dunbar factor, then a gas separator with an efficiency corresponding to the line it plots on is required at pump inlet. In such case, the separator efficiency is entered in

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the ESP design input dialog and pump calculations are repeated to ensure the point plots above the Dunbar factor line. The next step is to perform the design which involves selecting a pump, motor and cable which meet design parameters. Exit the plot, click on Done and then Design.

PROSPER filters out pumps, motors and cable that meet the design parameters from

a database. The data base can be accessed through Design | ESP | Pump database and the interface below is displayed.


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On this screen use Import | Append to import a pump database. There are some databases provided with the program in the \samples\ PROSPER directory. One can call up the motor and cable databases in a similar fashion. Return to the ESP design interface to select equipment that meet design criteria.

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From the available list of pumps, select the REDA SN8500 model. From the motors listed select the Reda 540_90-0_Int 400HP 2116V 113A motor..

Based on the selection available select #1 Copper cable. This stage completes the ESP design and the results are displayed on the same interface in terms of current required etc as shown below: A click on P l o t displays the pump performance curve which shows operational limits for the pump.


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The REDA SN8500 pump will require 136 stages (impellar - diffuser configurations) in series for the required head to deliver the fluids at the target rate and well head pressure. The point on this plot shows the design operating point on the pump performance plot. This concludes the new ESP design 3.2.5

STEP 4 : Use of QuickLook Diagnostic tool for ESP lift performance validation Ü

Note: In this section, the Quicklook diagnostic tool for ESP shall be used to validate a PROSPER ESP well model against measured data. Data available include rates and well head pressure as well as downhole pump intake and discharge pressures.

To perform the validation, select Matching | QuickLook . The measurements indicate a water cut of 60%. The pump is same as designed in the previous section. It will be assumed that the pump is not worn out and is still operating at a design frequency of 60Hz. Input the following test data. Tubing head pressure Liquid rate Water cut Produced GOR Static bottom hole pressure Pump depth Operating frequency Length of cable Gas separation efficiency Number of stages Pump wear factor

345 psig 6523 stb/day 60 % 392 scf/stb 2468 psig 7660 ft 60 Hz 7710 ft 0% 137 0 (fraction)

Downhole data: Pump discharge pressure (MD = 7660 ft) = 2725 psig Pump suction pressure (MD = 7660 ft) = 1025 psig

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To begin the calculation, select Calculate | Calculate and plot the pressure traverse along the well.


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The QuickLook principle calculates well pressure traverses for in two directions: one beginning from the wellhead and going to the sand face, and the other going from the sand-face up to the wellhead. If the model reproduced observed conditions in the well (assuming accurate test measurements), the pressure traverses should be identical. the pump is a tie point for the system i.e. where the inflow up to the pump and the lift above the pump are tied with each other. For a given wellhead pressure, the pump discharge pressure depends only on the weight and frictional loss of the fluid above the pump. It can be sen from the diagnostic plot that the pump discharge pressure calculated from the downward traverse is slightly lower than the measured test point (blue point). This section of the well can be considered as a naturally flowing well with bottomhole pressure equal to the pump discharge pressure. Thus to match the downward discharge pressure point with the measured point, the model can be switched back to natural flowing conditions and the flow correlations tuned to reproduce the measured pressure profile from top of the well to pump discharge point. The test data is given below. Tubing Head Pressure: Tubing Head Temperature: Water Cut: Liquid Rate: Gauge Depth: Gauge Pressure: GOR: IPM Tutorials

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156

0 scf/STB

Enter these data in the VLP/IPR Matching section:

Perform a Correlation Comparison to quality check the test data. The test data point is within the limits given by the Duns and Ros Modified and Fancher and Brown correlations, as shown in the following plot:

After data quality check, the correlation which gives pressure profile closest to data point can be selected and then matched to the data point. The choice of the correlation and VLP match is done following the guidelines given © 1990-2009 Petroleum Experts Limited

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by the PROSPER manual and previous examples for natural flowing wells. Back to the VLP/IPR screen, click on Match VLP and match the Petroleum Experts 2 correlation.

The match parameters are calculated and displayed by clicking on Statistics.

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With the well section above the pump matched to measured data, re-select the ESP artificial lift method from Options interface and go to the Quicklook section. Click on Calculate ôCalculate, then Plot. The following QuickLook plot is displayed:


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As can be seen, the measured and calculated discharge pressures are matched. The next step is to obtain a match on the inlet conditions of the pump. The above plot shows that the DP across the pump calculated in the downward gradient is greater than the measured pump DP (as indicated by the distance between the two blue squares). The likely cause of the deviation could be due to pump wear, which decreases the pump performance. If a pump wear factor of 18% (0.18) is input on the Quicklook main interface and the calculations re-performed, the following diagnostic plot is obtained.

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The downward gradient is now matched (green curve). The final step is to obtain a match on the upward gradient. The upward gradient depends on the Inflow as it is calculated starting from the flowing bottom hole pressure obtained from the IPR. The upward gradient shows greater pressures than the downward gradient. Parameters to change depends on IPR model being used and the engineers knowlege of the system. Reduce the PI for the well to 6.3 stb/day/ psi in the IPR section and perform the calculations again in the Quicklook section.

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A match is now obtained for both downward and upward pressure traverses. This exercise shows how the quick look diagnostic tool can be sued to investigate/ troubleshoot performance of ESP lifted wells provided reliable flow and pressure measurements are available. Save this file as ESPG1.out in a suitable directory.

3.3

MBAL Gas History Matching Example This tutorial example is provides more insight into MBAL following on from the MBAL Gas Reservoir Example of the Dexterity section.

3.3.1

Objectives

The focus of the example is to match a gas reservoir model in MBAL to production history. The history match process will provide more information about original volumes of gas in place and drive mechanisms acting. Knowledge of the drive mechanisms acting will increase one's understanding of the reservoir’s potential production. Relative permeabilities for gas and water will be estimated by matching historical fractional water production to simulated water production (from the model) and this shall be tested by performing a prediction calculation. Input data required is production and pressure history data. This is contained in GASRES2.xls located in C:\Program Files\Petroleum Experts\IPM 7.x\Samples \Worked Examples\Physics Examples\Gas history matching.

3.3.1.1

Learning topics


· History match a MBAL tank model · Analyse a graphical material balance plot · Tune the model parameters to a suitable starting point for the regression · Perform regression on parameters of most uncertainity · Quality check history match · Prepare model for predictions through fractional flow matching · Quality check fractional flow match. 3.3.1.2

Executive summary

The following steps shall be taken to achieve the objective.


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· Input production history · Conduct history match · Analyse graphical plots · Tune tank parameters and Input aquifer model · Perform regression · Verify quality of history match - Run Simulation · Conduct fractional flow matching · Verify fractional flow match - Run prediction 3.3.2

STEP 1 : Initialise MBAL

Start the MBAL program by running MBAL.EXE, which can be found in the PETEX directory (The default location is usually C:\Program Files\Petroleum Experts\IPM 7.0). See the MBAL manual for more details on how to start MBAL. Check that the current version of MBAL has been loaded. Select Help | About MBAL Package to check the version number. Select File | Open to open the file created from the MBAL Gas Reservoir Example in the Dexterity section - GASRES.MBI. Save this as a new file (GASRES2.MBI) using File | Save As . The model was previously built with an estimated GIIP. With production data this can be better estimated along with drive mechanisms acting. 3.3.3

STEP 2 : Input Production History Data

Production history data is entered and an aquifer model is initialised in this section. Enter the production history shown below in Table 1 by selecting Input | Tank Data and selecting the Production History tab. Reservoi Cum. Cum. Cum. r Gas Water Gas Time Pressure Produce Produced Injected d date d/m/ psig Bscf MMSTB MMscf y

01/01/199 8 01/04/199 8 01/07/199 8 01/10/199 8 01/01/199 IPM Tutorials

Cum. Water Injected MMSTB

11500

0.000

0

0

0

10866

23.109

0.0145645

0

0

10381

44.684

0.0285966

0

0

9967

65.298

0.0424057

0

0

9598

84.849

0.0559903

0

0 October, 2009

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9 01/04/199 9 01/07/199 9 01/10/199 9 01/01/200 0 01/04/200 0 01/07/200 0 01/10/200 0 01/01/200 1 01/04/200 1 01/07/200 1 01/10/200 1 01/01/200 2 01/04/200 2 01/07/200 2 01/10/200 2 01/01/200 3

9267

103.049

0.0692967

0

0

8955

120.618

0.0830781

0

0

8659

137.575

0.0976719

0

0

8380

153.762

0.113271

0

0

8121

168.873

0.129811

0

0

7874

183.494

0.148142

0

0

7636

197.644

0.168577

0

0

7410

211.188

0.191149

0

0

7200

223.875

0.215463

0

0

6998

236.155

0.242381

0

0

6805

248.039

0.272059

0

0

6621

259.401

0.304208

0

0

6449

270.151

0.338412

0

0

6285

280.445

0.37498

0

0

6127

290.419

0.414325

0

0

5977

299.974

0.455474

0

0

164

This data is also contained in an EXCEL spreadsheet named GASRES2.XLS and the data (cells A5:F25) may be copied and pasted into MBAL using a right mouse click on the prameters tabs (top) of the production history spreadsheet. The spreadsheet is located in C:\Program Files\Petroleum Experts\IPM 7\Samples \Worked Examples\Physics Examples\GAS History Matching Alternatively, any one of the production history spreadsheet row numbers can be right-clicked then from the pop-up menu select Paste . NOTE: If a paste function is done in the first spreadsheet cell then all the data will be placed in the single cell. Delete the data by using the B a ck s p ac e keyboard button and use one of the above data paste conventions. © 1990-2009 Petroleum Experts Limited

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NOTE: It is very important to check that the units for the input data are consistent with those on the input screen of MBAL. The units can be changed in MBAL from the main menu by clicking on UNITS or by clicking on the unit itself on the production data interface.

As seen from the table, the Cummulative gas producted is in units of Bscf and this unit is changed on the parameter tab before the data is pasted.

3.3.4

STEP 3 : Introduction to Material Balance concepts

A very brief introduction to the material balance method is included here. The governing principal is volume conservation as the reservoir is produced. This may be restated as: The volume of material removed by production at reservoir conditions is replaced by fluid/formation expansion and possible aquifer influx.

The equation below represents this volume (material) balance at reservoir conditions (pressure and temperature): F = N.Et + We F is the produced fluid volume at reservoir conditions. Good production history and PVT is required to estimate this quantity. N is the original oil/gas volume in place, which can be estimated by geological investigations. Et is the expansion of the reservoir fluid and water, and formation rock compaction following the depressurisation of the reservoir as it is produced. Good reservoir pressure history and PVT is required to estimate Et. Note that for oils, good PVT (Bo) above the bubble point is especially important, since the compressibility of undersaturated liquid oils is relatively small. We is the volume of aquifer water entering the initial reservoir volume.

In general, if good PVT , production and pressure history is available, F and Et are reasonably well known. Also, an initial estimate of N can usually be made. The objective of history match then is to refine correlations for We and the value of N to match the production data. The material balance equation above can be rearranged and a non-linear regression performed on parameters of most uncertainty within it e. g. on N and aquifer model parameters. The quality of the PVT and production history data is vital to the material balance calculations. For simplicity, this example uses an matched Black Oil PVT and a fictitious production history.

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STEP 4 : Material Balance History Matching

The production history data will be matched to a material balance model using nonlinear regression and more importantly the user's engineering judgement and knowledge of the system. The drive mechanisms within the reservoir and the Original Gas In Place (OGIP) will be estimated. The History Matching process starts with an initial assumption of no aquifer. Thus on the Tank Input data screen, select No Aquifer. Select History Matching | All . Three screens appear graphically illustrating the fit of the material balance model to the production data and reservoir pressure. It is suggested that the MBAL window is made full screen to aid viewing.

The material balance model is defined by the correlations and parameters entered in the Input | Tank Data screens. All of these may be altered at any time to improve the fit, but only the OGIP and the aquifer model parameters may be modified by nonlinear regression. This reflects the observation that these are generally the least well known variables. It is very important that a systematic methodology is followed, based on an understanding of the material balance model, rather than a series of regressions. It should be understood that the regression solutions are not necessarily unique and work better if their values prior to regression are not too far from a solution. Therefore the interpretation of the graphical representations of the material balance model must be used to refine the model before a regression is performed.


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Currently an aquifer model has not been included in the model as characteristic plots obtained by re-arranging the material balance equation (graphical methods) which may indicate the presence of an aquifer shall first be checked. Highlight the Graphical Method window by clicking the left mouse button within its title bar, and select Method | Cole ((F-We)/Et). Recall the material balance equation can be written as (F-We)/Et = N. (when We = 0, F/Et = N). If the material balance model was well fitted to the production data then the Cole plot should be a horizontal line with an intercept equal to N (OGIP).

The plot shows an initial rise which indicates an increasing apparent value for N. This means the expansion (Et) of the reservoir fluids/formation alone is not sufficient to maintain the reservoir pressure. In other words, there is more energy in the reservoir than currently predicted by the material balance model. These equivalent statements imply the reservoir pressure is being maintained by another mechanism, which most likely is an aquifer. Also note the shape of the Cole plot. There is an initial rise, a stabilization and a later decline. This can be interpreted as the aquifer inflow slowing at around data point 5 and stopping near data point 10. This means that around this time the outer boundary of the aquifer has been ‘felt’. At early times, the well will not feel the influence of the aquifer. Therefore the early values on the Cole curve indicate minimum values for N. Select Display | Scales and set the Y-axis bottom value to 600 Bscf (which is the OGIP entered in the tank input screen) and select Done. An extrapolation of the Cole curve towards the Y axis is difficult, emphasizing the importance of early data recording. However, as an IPM Tutorials

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initial assumption an extrapolation to the Y-axis would suggest a value for N larger than 600 Bscf, perhaps nearer 750 Bscf. The original volumes of gas in place shall be updated to 750 Bscf and an aquifer model input. The following data for the aquifer can be used as a starting point: Model Hurst-van Everdingen Modified System Radial Aquifer Reservoir thickness 100 ft Reservoir radius 5000 ft Outer / Inner radius ratio 5 Encroachment angle 360 degrees Aquifer permeability 20 md

Conducting the history match again, the following plots are obtained.


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From the Graphical Method (Cole plot) screen shown above it is clear that the aquifer that has been added is too strong, it is providing too much energy to the system (i.e. the trend line goes below the horizontal). The extrapolation of the Cole curve to the Y-axis suggests a reduced OGIP (N). The WD function Plot screen (top left screen) shall be reviewed. This shows a dimensionless time (tD) and dimensionless aquifer inflow volume (Q). The ‘elbow’ of this curve occurs at the point where the aquifer cannot supply additional water; the boundary of the aquifer has been ‘felt’. Recall that the initial Cole curve suggested this occurred between data points 5 and 10. Move the cursor within the WD function Plot screen and double click using the left mouse button. This alters the Outer/Inner Radius parameter of the aquifer model, altering the displays in the other Method screens. In particular, notice that the Analytical Method gas production/pressure curve moves. By double left clicking in the WD function plot screen, try to select an aquifer Outer/Inner Radius parameter that shows a reasonable fit to the production displayed in the Analytical Method screen. An Outer/Inner Radius of approximately 2.1 works quite well, but the ‘elbow’ on the WD function Plot is not between data points 5 and 10. Highlight the Analytical Method window and select Regression from the toolbar. Set the Outer/Inner Radius to 2.1 in the start (left) column and select Done to view the results.

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The data points at very early times may only be reflecting responses from regions in the vicinity of the well and don’t necessarily show responses of the entire reservoir, therefore the material balance would not be expected to show the complete OGIP until the pressure signal from the producing well has had time to permeate the entire reservoir It is possible that the Graphical Method screen is showing this effect at early times. © 1990-2009 Petroleum Experts Limited

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The signal time to permeate the reservoir can be estimated from the diffusivity and reservoir dimensions. The diffusivity, D=k/ jmc (ft2s-1) relates the radial pressure response at a distance r and time t from the well source by the equation P µexp(-r 2 /4Dt). For this example the first data point shown (point 2) is one year after the start of production and can probably be expected to reflect the whole reservoir’s response, suggesting that the aquifer model still requires some fine tuning. Note also that the ‘elbow’ of the WD Function Plot is not reflecting correctly the time at which the aquifer energy is exhausted. However, recognizing the points noted above, the material balance model is now not too far from being consistent with the production data and non-linear regression may be used to refine the model parameters. Highlight the Analytical Method window and click on Regression. Check the Gas in Place, Outer/Inner Radius, Encroachment Angle and Aquifer Permeability boxes to regress on.

Select Calc to start the regression. When it finishes, copy the B e s t F i t values to the Start values by clicking the left pointing arrows in the above screen shot or simply Accept all fits. Select Done to view the changes. It is important not to regress on combinations of parameters that are simply multiplied by each other in the aquifer model. For example, the Hurst-van Everdingen aquifer constant contains the product of porosity, reservoir thickness, encroachment angle and the square of the original reservoir radius. If a regression is performed on pairs of these parameters, then the regression will not converge easily, particularly if the initial values are not close to a solution.

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As seen from above, a good match is obtained, the aquifer model and OGIP are consistent with the production history. Please note that although the actual values calculated for the aquifer model describe the aquifer fairly well, the individual parameter values do not in themselves necessarily correspond to reality. These parameters are not a unique set that characterize the aquifer. They are simply used used to describe the aquifer response. Select Finish | File | Save to save the file.

3.3.6

STEP 5 : Relative Permeability Matching

In this section, the effective relative permeability of water is calculated. This pseudorelative perms will be used to determine fractional flow of water during a prediction run. It will be obtained by matching the fractional water flow obtained from the production history to the fractional water flow as defined by the initial pseudo-rel perms entered under tank parameters. Both fractional flows are plotted against fluid saturations calculated by a material balance simulation. The relative permeability data input under tank parameters were not used during the material balance history matching and are also not used during the simulation calculation, since the produced water and gas are input as part of the production history. The simulation step provides water saturation within the tank model, resulting from a material balance simulation. The next step is to perform a material balance simulation. This process achieves two objectives:


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· Verifies the quality of the history match · Calculates historical tank fluid saturations Select H is t o r y M at c h in g | Ru n Sim u latio n | Calc to run a material balance simulation of the production history. Select OK when the calculation has completed.

Plot the simulation and history tank pressures by selecting Plot | History.

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With a good match obtained between the historical and simulated tank pressures, fractional flow matching can now be conducted. Return to the main MBAL display by clicking D o n e . Next, select H i s t o r y M a t c h i n g | to display the matching screen. Fw Matching


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Within this screen, the fractional water flow is plotted as a function of water saturation. The water breakthrough point can be set by a double left click at an appropriate saturation (a dashed green line is shown at the new breakthrough saturation). Note that a breakthrough point below the connate water saturation (indicated by a grey line) is not possible. Additionally parameter values can be entered by selecting Parameters . Leave the water breakthrough saturation at the connate water saturation (0.2). A region of the display can be enlarged by holding down the left mouse button and dragging it across the desired region. The original display can be redrawn by selecting Red raw from the plot menu. Production history data points may be selected by holding down the right mouse button and dragging it to select the desired points. The weighting of the selected points may be altered, or excluded from use in the regression. Select Regress , then Parameters to display the matched parameters. Select F | Yes to save the matched Corey coefficients. inish

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It is now desirable to perform a Material Balance Calculation to check that the fractional flow of water is sufficiently well characterized by the matched relative permeability model. This objective will be achieved by re-simulating the history such that produced water is not defined by the historical values but as obtained from the matched fractional flow (i.e. using the pseudo-rel perms). A material balance prediction (over the history period) will be done for this purpose. This will require a production history of the main fluid phase in the tank and these will be put into the model to calculate the evolution of other fluid phases as determined by the pseudorel perms. Of particular interest will be the predicted WGR (Water Gas Ratio) for this example. Select Production Prediction | Prediction Setup and set the prediction method as shown below and select Done. Ensure that Use Relative Permeabilities is checked, prediction is from Start of production and the Prediction End is set to End of Production History.


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Select Production Prediction | Production and Constraints and copy the production gas history (by selecting Copy) into the production constraint screen and select Done.

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Select Production Prediction | Reporting Schedule. The reporting frequency of the results generated by MBAL are specified here. Select A u t o m a t i c . Hence, click on Done to accept automatic reporting. Next select Prediction | Run Prediction | Calc and OK | Plot when the calculation has completed. Select Variables and highlight streams Simulation and Prediction, and plot Pressure , then select Done to view the plot.


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For this example, the history, simulation and prediction (history re-simulated using fractional flows) give a good match and this gives some confidence in future predictions with the model. If the prediction does not model the fractional productions well, then the fractional flow can be re-matched using different data point weighting's or Corey parameters altered by hand. Select Finish | Done | File | Save to complete this tutorial example.

3.4

MBAL Oil History Matching Example This example presumes that the user is familiar with setting up single tank models in MBAL. The exercise focuses on the design of a tank model for an oil reservoir.

3.4.1

Objectives

The focus of the example is to model an oil reservoir using material balance techniques in MBAL, provide representative estimates of original volumes in place and drive mechanisms acting by history matching the model to pressure and production data. Knowledge of the drive mechanisms acting will increase one's understanding of the reservoir’s potential production. Relative permeabilities for gas and water will be estimated by matching historical fractional water production to simulated water production (from the model) and this shall be tested by performing a prediction calculation.

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Input data required is production and pressure history data. This is contained in GASRES2.xls located in C:\Program Files\Petroleum Experts\IPM 7.x\Samples \Worked Examples\Physics Examples\Oil history matching.

3.4.1.1

Learning topics


· Design a tank model for an oil reservoir. · Quality check production and pressure data. · Perform history match. · Analyse a graphical graphical material balance balance plot · Tune the model parameters to a suitable starting point for the regression · Perform regression on parameters of most uncertainity · Quality check history match · Prepare model for predictions through fractional flow matching · Quality check fractional flow match. · Perform production prediction using the history matched model.

3.4.1.2

Executive Summary

The following steps shall be taken to achieve the objective.

· Define MBAL reservoir modeling options/objectives · Define fluid PVT model parameters rs for volumes volumes and saturati saturations, ons, initial conditi conditions ons of pressur pressure e · Input tank paramete and temperature e.t.c · Input production history · Conduct history match · Analyse graphical graphical plots plots · Tune tank parameters and Input aquifer model · Perform regression · Verify quality of history match - Run Simulation · Conduct fractional flow matching · Verify fractional flow match - Run prediction · Perform production prediction 3.4.2 4.2

STEP 1 : Model Setup tup

· Start MBAL and select the menu option File | New . · On the main menu, click on Tools | Material Balance . · On the menu bar click on Options and following interface appears. Select the © 1990-2009 Petroleum Experts Limited

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following options as shown below:

From From this this inter interfac face, e, a single single tank model model has has been been chose chosen n with with oil oil defin defined ed as the main main fluid fluid and and produ producti ction on histo history ry will will be provid provided ed as a cummu cummula lativ tive e for for the entir entire e reservoir. Next on the main menu, click on PVT | Fluid Properties and input the following PVT properties of the reservoir fluid expressed at standard conditions and match Black oil correlations to the bubble point conditions of the fluid. (@ 250 deg F)

· · · · · · · ·

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Bubble point (P b)

2200 psig

Solution GOR Oil FVF @ Pb

500 SCF/STB 1.32 RB/STB

Oil Viscosity @ P b

0.4 cP

Oil gravity Gas gravity Water Salinity No Impurities

39 API 0.798 100,000 PPM

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In the PVT section, any set of black oil correlations can be used to define the PVT prop roperti ertie es of the fluid luid.. With ith lab laborat ratory mea measur suremen ments availa ailab ble, le, the the blac lack oil correlat correlations ions will be matched matched to them and the best correla correlation tion which reproduce reproduces s the PVT behaviour of the fluid will be selected. PVT matching is conducted by selecting the Match button and the following screen appea ppears rs and we can ent enter mea measure ured data at bubb ubble point int as indic dicate ated in the following screen:


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With the data entered entered,, click on Match to proceed to the regression interface. Select Match All on the bottom and then Calc. This matches all the correlations available to measured data.

With the matchi matching ng conc conclud luded, ed, click click on Match where the regress regression ion match match Match Param Param where parameters 1 and 2; and standard deviation are reported for each correlation. For IPM Tutorials

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this example, Glaso correlation gives the best match for Pb, Rs and Bo while Beggs correlation will be used for viscosity calculations.

This step completes teh reservoir fluid PVT description. The next step is to define reservoir parameters for the tank model. On the main menu bar click on Input | Tank Data, where the following information about the reservoir is entered. Tank type Tank name Temperature Initial pressure Porosity Connate water saturation Water compressibility Initial gas cap Original oil in place Start of production

Oil Tank01 250 degree F 4000 psig 0.23 0.25 Use Corr 0 206 MMSTB 01/01/1998


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On the tank parameters interface, the reeservoir fluid volumes and initial pressure and temperature conditions are defined. The reservoir is initially undersaturated as indicated by an initial gas cap of zero (i.e. OGIP/OOIP ratio). In addition, from the fluid PVT model, bubble point pressure is 2200psi which indicates that reservoir is initially undersaturated and no free gas exists at initial conditions. Based on fluid PVT model, the program determines the initial state of the reservoir. In case the reservoir is saturated, an initial estimate of the gas cap size is required. Also, an initial estimate of volumes of oil in place as obtained from geological surveys is required and a production start date. Next, information about aquifer support for the reservoir is required. As there is yet no evidence to suggest the presence of an aquifer, this will be left as N o n e . The next information required is about the formation rock compressibility to determine energy contribution due to Hydrocarbon pore volume reduction. This can be user-specified, obtained from a porosity correlation or variable in terms of pressure. For this example, it shall be determined from porosity correlations.

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The next data required is the relative permeability data. Relative permeability data is used in prediction calculations only. It is used to determine the fractional flow of water and/or gas which depend on the water and gas saturation in the tank. This defines the evolution of WC and/or GOR. If an initial gas cap exists and it is being produced from, the total reservoir volume including the gas cap should be used to obtain tank saturation (i.e. connate and irreducible saturations should be entered relative to the entire reservoir system). Relative permeability can be entered in form of tables or Corey functions. The following data based on Corey functions is input. Phas e

Residual Saturation (fraction)

End Exponen Point t (fraction)

Wate r

0.25

0.7

1.5

Oil

0.15

0.8

1.3

Gas

0.02

0.9

1


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Water and gas sweep efficiency sections available on the Rel perms interface can be used to estimate speeds at which water and gas contacts move when monitor contacts option is selected on the Tank Parameters Interface . The production and pressure history data available are entered on the production history tab. This data is contained in the Microsoft Excel file OILRES1.XLS located in C:\Program Files\Petroleum Experts\IPM 6\Samples\Worked Examples\Physics Examples\Oil history matching.

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The data is copied from the file and pasted in this section using a right-click on the parameters tab (Top) of the interface and selecting 'Paste'. Alternatively, any of the row serial numbers can be right-clicked upon and the option to paste the data is available.

This concludes model setup. Save the file as OilRes1.mbi in a directory of choice. Next step is to perform history match. 3.4.3

STEP 2 : Matching to Production History data in MBAL

As a quality control step, the production history data can be compared with the PVT model for consistency. From PVT model, bubble point pressure = 2200psi and solution GOR = 500scf/stb. Clicking on Work with GOR at the bottom of the production history interface converts Cummulative gas rates into produced GOR values.


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By scrolling down across the data, it can be seen that the reservoir is undersaturated throughout the history i.e pressure is always above the bubble point of 2200 psig. There is no free gas in the tank and hence the producing GOR equals solution GOR. Indeed in this case the gas rates coverted into GOR values give approximately 500 SCF/STB. This shows that the data is consistent with the PVT. In cases where the cumulative GOR is not consistent with PVT data, both should be reviewed. With consistent production history and PVT data, the history match can be conducted. It is important to note that a model which closely reproduces historical behaviour of the reservoir when different history match techniques are employed is what is sought after. Select History Matching | All. This produces the following plots.

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The first plot is the Energy Plot which shows the contribution of various drive mechanisms towards production with time. The second plot is the Campbell Plot which is a graphical (diagnostic) plot. Campbell analysis re-arranges the material balance equation such that a plot of the ratio of net produced volumes (Prod - Aquifer Influx and/or injection) divided by expansion terms yields a horizontal line with an intercept equal to initial volumes in place. The Campbell plot is the default plot in MBAL. There are other graphical methods that can be selected by clicking on Method on the menu of the graphical plot The third plot is the Analytical Plot. This is a plot of tank pressure against cummulative primary phase produced (in this case oil). The data points are the historical pressure and cummulative rate data. The blue line indicates the response of the MBAL model according to the data entered in the Tank Data screen. The Campbell plot shows some form of energy acting (initial increase and then a stabilisation). This is most likely due to an aquifer acting and thus an aquifer model will be input into the model. The following aquifer properties are input as shown below and performing the history match again gives the following profiles.


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A look at the analytical plot, indicates that with the current aquifer model, the tank model predicts production rates higher than those actually observed. This means that the aquifer is weaker in reality than the aquifer model being used. The strength of the aquifer model can be decreased by reducing the aquifer inner/outer radius ratio (r D) on the tank aquifer model interface. We can decrease the strength of the aquifer either by accessing on the tool bar of the previous screen Input | Tank data and decreasing the aquifer inner to outer radius ratio (r D). This same objective can be achieved in the Q(tD) versus tD - Radial Aquifer plot. Double click on the plot to change the to change the profile to a smaller r D value of 4.0 such that on the analytical plot, the actual history points and the model response fairly match as shown below.


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From the analytical plot, it can be seen that a fairly good match is obtained between the model and historical data. However from the Campbell plot (graphical method) a horizontal profile was not obtained. It is thus recommended to perform history match while viewing all the different history match techniques at thesame time (i.e. History match| All) so that a model which reproduces reality across all the techniques is selected. With a close match between model and measured data as seen on the analytical plot, a regression can be performed on other parameters in the model to produce a match across all the techniques (graphical and analytical). Click on Regression on the analytical plot menu bar. Select the following parameters to be regressed upon.

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Parameters of least uncertainty are chosen for the regression (i.e fluids in place and aquifer parameters). It is important not to regress on combinations of parameters that are simply multiplied by each other in the aquifer model. For example, the Hurst-van Everdingen aquifer constant contains the product of porosity, reservoir thickness, encroachment angle and the square of the original reservoir radius. If a regression is performed on pairs of these parameters, then the regression will not converge easily, particularly if the initial values are not close to a solution. Once the regression is complete, select the parameters by clicking on Accept all fits | Done.


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The following plots are obtained.

A satisfactory match is now obtained across the graphical and analytical history match methods. Save the file as Oilres.mbi in a directory of choice.

3.4.4

STEP 3 : Sensitivity Analysis

With the history match completed, a model is obtained with certain parameters for volumes in place and drive mechanisms acting. It is imperative to verify the regressed figures using both engineering judgement and knowledge of the system as well as conducting some sensitivity analysis on the model parameters. In sensitivity analysis the sensitivity of the model response to changes in parameters obtained through history match/regression are checked. A sensitivity analysis can be performed by clicking on History matching | Sensitivity on the main menu. The following interface appears and the effect of a change in OOIP between a range of 180 and 250 MMstb shall be investigated.

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Click on Plot to obtain the sensitivity profile.

On the x-axis is the OIP and on the y-axis is the standard deviation in terms of predicted production rates over the history. The presence of a minimum shows the uniqueness of the solution. Similarly, a sensitivity analyses on other parameters of drive mechanism acting like the aquifer parameters for this case can be performed.


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STEP 4 : History Match Quality Check

With a sensitivity analysis done, the next step is to check the quality of the history match. This is achieved using the Run Simulation step. The fundamental difference in the calculation for the Analytical Method of History Matching and the Run Simulation is explained in the following paragraphs. The analytical method takes the reservoir pressure and cummulative secondary and/ or tertiary fluid phases (water and gas for this case) from the production history; inserts these into the model and calculates the cummulative volumes of main fluid phase (oil for this case). This is plotted with the reservoir pressure and compared with the historical cummulative oil produced. A regression in the analytical method seeks to match the calculated cummulative oil volumes with historical cummulative oil volumes by varying some parameters in the model. The simulation step on the other hand seeks to reproduce the historical decline of the reservoir. This step takes the various fluid phase rates from history data (oil, gas and water for this case), inserts these into the model and obtains the pressure decline. The calculated pressure response is compared with historical pressure decline. S good match between these two parameters will indicate a good history match as model is able to represent reservoir behaviour. Select History Matching | Run Simulation | Calc., the program does calculations. At the end of the calculation select P l o t . From the main plot menu select Variables then highlight both the History and Simulation folders to compare the data.

A plot of tank pressure with time shows a good match between model and historical data. Ü

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various development alternatives, fractional flow matching should be conducted. Fractional flow matching step generates pseudo-rel perm curves that are matched to historical water and/orgas production, so that future evolution of these parameters can be accurately estimated. Please refer to previous example on Gas history matching for more information.

3.5

MBAL Production Prediction Example This example shows how to perform prediction runs on a gas reservoir MBAL. model which has been history matched. The history data was obtained for 3 wells and this was entered on a well basis ( Production History- By Well option). The data was cumulated for the entire tank and history match conducted. All the example files are located in: C:\Program Files\Petroleum Experts\IPM 7.x\Samples\Worked Examples\Physics Examples\Production and Prediction

3.5.1

Objectives Statement of the problem An MBAL model for a gas reservoir with production history obtained for 3 wells has been created and history match performed with the cummulative production history for the tank. A production prediction is to be performed on the model considering two development scenarios. Case 1: Following the historical/current production pattern i.e. with a FWHP of 800 psig Case 2: Reduce the well head pressure to 100 psig as from 01/01/2004 Input Data Well Inflo w Data

For this example, each wells Inflow performance is represented by the C & n model. Any analytical gas IPR model can be equated to the C & n method. For more details on Inflow models, please refer to the PROSPER manual. Well Name

C- factor (Mscf/d/ psi2)

n-Exponent

Producer#1

0.027

0.85

Producer#2

0.002

0.95

Producer#3

0.005

0.9

Generic Well Outflo w tables:


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It will be assumed that all wells in this example have the same lift tables. Lift tables can be generated in PROSPER and then imported in MBAL. These have already been prepared and can be found in: C:\Program Files\Petroleum Experts\IPM 7.0\Samples\Worked Example\Physics Examples\Production and Prediction\GasTank Well Lift Tables.TPD 3.5.1.1

Learning topics


· Perform production prediction using well models · Define prediction well models - IPR and VLP models · Assign matched fractional flow rel perms by well · Saving prediction runs

3.5.1.2

Executive Summary

The following steps shall be taken to achieve the objective. Starting with a matched gas tank model in terms of production history and fractional flow

· Define well models · Input IPR model · Assign individual matched fractional flows to each well · Input VLP model - Import lift curves · Input production schedule · Run prediction 3.5.2

STEP 1 : Production Prediction Setup

The starting point for this example is gasTank1.mbi file located in the above mentioned directory. Step-by-Step procedure for a prediction run in MBAL Step 1: Prediction set-up

In order to perform a prediction, select Production Prediction | Prediction Setup and make the following changes:

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Select D o n e to complete this.

3.5.3

STEP 2 : Boundary conditions

Select Production Prediction | Production and Constraints and enter date and Manifold Pressure as shown in the screenshot below:


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The manifold pressure corresponds to the furthest downstream node pressure which the well produces against. In this example, the manifold pressure is the well head pressure. Select Done. 3.5.4

STEP 3 : Well Type Definition

This is where the well model is defined. Each well is defined by a VLP (Vertical lift performance) and an IPR (Inflow Performance Relationship). Select Production Prediction | Well Type Definition, the following screen is accessed:

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Clicking the “ ” button to add a well. The well name can be changed to “Producer#1P” as shown below. The well type is also set as “Dry Gas Producer”.


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Select the Next button to proceed to the Inflow section. 3.5.5

STEP 4 : Inflow Performance

The C & n IPR mdoel is selected and the parameters input as shown.

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Since a well model is being used to predict main fluid phase, the eveolution of other fluid phases are obtained from the pseudo-rel perms. The pseudo-rel perms have been matched individually for each well since production history was obtained on a well basis. Details on how to match historical fractional flow by well is provided later. To assign the pseudo relative permeabilities matched for the wells during the fractional flow matching, select Use Rel perm 1 | Edit | Copy . A list of all the permeability tables available in the MBAL model is displayed:


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Here select Material balance - Well Producer#1 and then select Copy and then the Corey parameters are assigned to the well. Now click on Done. MBAL asks if the water breakthrough saturation is to be copied; select Yes:

Click on Next and Next to go to the outflow section. Note: Generation of pseudo-rel perms when history data is provided on a well basis is outlined below. After running a MBAL simulation, select History Matching | Fw Matching from the main menu toolbar. The follow plot is displayed:

From the menu toolbar of the plot screen, select Well, and then the well whose fractional flow is to be matched.

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By default, the breakthrough saturation (green line) is at the value entered under the Rel perm data section of Tank data. This value can be changed by double-clicking on the plot area to the point corresponding to the desired breakthrough water saturation. Click on Regress, so that the program can perform a regression to match the fractional flow as computed from pseudo-rel perms entered under tank data (blue line) to the historical fractional flow (data points) by varying corey function parameters.


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STEP 5 : Outflow Performance

The Vertical lift curves for the wells are imported into the model in the Outflow performance section.

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On this interface, click on the Edit button and then select Import. Browse for the lift curve file (*.tpd file) provided in C:\Program Files\Petroleum Experts\IPM 7.0 \Samples\Worked Example\Physics Examples\Production and Prediction\GasTank Well Lift Tables.TPD . TPD files are lift tables in Ascii format for Petroleum Experts applications ( GAP, REVEAL, MBAL) and have been made from the respective PROSPER well models.

Click on Open and a statistics of imported variables is shown.

Select Done | Done and this completes the setup of this well. Repeat the same process for two other wells using the data given in above sections. Please note that the same .tpd file will be used for all the wells.


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With the data for all the prediction three wells entered, click on Done to go back to the main interface. The main screen now shows three history wells and three prediction wells. Please note that there are only three wells in reality. These have only been split into history and prediction wells. Note the difference between the wells. It is further advisable to differentiate between history and prediction wells in terms of nomenclature e.g. An additional "P" for prediction wells.

3.5.7

STEP 6 : Well Schedule

To schedule start times of the wells, select Production Prediction | Well Schedule and input the following data: Wells can be activated/deactivated by clicking on the respective row serial number.

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Click on Done to validate the screen. 3.5.8

STEP 7 : Reporting frequency

Select Production Prediction | Reporting Schedule. The reporting frequency is set to "Automatic" and the option to "Keep history" is selected.


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The “Keep History” button allows to have the full history stream along with the prediction stream for comparison purposes. Click on Done to exit the screen. 3.5.9

STEP 8 : Production prediction

Click on Production Prediction | Run Prediction | Calculate, then Ok. The results of the calculation are displayed:

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Click on Plot | Variables and make the following choices:

Afterwards, click on Done. The following plot is displayed:


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It is now possible to analyse production through different development schemes. To do this, one can save the results for comparison From the plot toolbar select Finish. It is possible to save the results of each prediction, so that they can be reviewed later and compared to other scenarios. In the Run Prediction screen, click on Save:

Then click on Add and input a stream name e.g. Case 1

Select Done | Done to complete this. This completes the first exercise objective i.e. Case 1. The second exercise objective can be achieved as follows Choose Production Prediction | Production and Constraints, and enter the new data for Case 2:

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Select Done to complete this. As previously done, run the prediction by clicking on Production Prediction | Run Prediction | Calculate. Save the results as Case 2 using Save | Add.

Both development options can now be compared in terms of average gas rate and cummulative gas production by clicking on Plot |Variables on the Run production prediction interface and selecting Case 1 and 2.


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Then Done and the following plot is displayed:

This plot shows a comparison between Case 1 and Case 2. This completes the exercise objectives. Please save the file as: GasTank1_Complete.mbi in a suitable directory. IPM Tutorials

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Tutorial Complete

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