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PRODUCTION OPTIMIZATION OPTIMIZATION OF A MATURE MATURE FIELD: USING US ING NODAL ANALYSIS ANALYSIS FOR FO R IMPROVING GAS LIFT WELLS Research Proposal · Proposal · March 2017 DOI: 10.13140/RG.2.2.27895.62881
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A PROPOSAL ON THE PROJECT TOPIC PRODUCTION OPTIMIZATION OF A MATURE FIELD: USING NODAL ANALYSIS FOR IMPROVING GAS LIFT WELLS BY
OKORO FAITH EFEREMO
INTRODUCTION
Hydrocarbons are produced from wells that penetrate geological formations rich on oil and gas. The wells are perforated in the oil and gas bearing zones. The hydrocarbons can flow to the surface provided the reservoir pressure is high enough to overcome the back pressure from the flowing fluid column in the well and the surface facilities Any well production is drilled and completed to move the oil or gas from its original location in the reservoir to the stock tank or sales line. Movement or transport of these fluids requires energy to overcome friction losses in the systems and to lift the products to the surface. The fluids must travel through the reservoir and the piping system and ultimately flow into a separator for gas-liquid separation. The production system can be relatively simple or can include many components in which energy or pressure losses occur. The production rate or deliverability of a well can often be severely restricted by the performance of only on e component in the system. If the effect of each component on the total system performance can be isolated, the system performance can be optimized in the most economical way. Some reasons for artificial lift include: Well’s producing capacity was actually being restricted because the tubing or flowline was too small. Another example of errors in completion de sign is to install too large tubing. This often happens on wells that are expected to produce at high oscillating flow. Too large tubing can actually reduce rate at which a well will flow. This can cause the well to load up with liquids and die, which necessitates the early installation of artificial lift equipment or compression. Most wells completed in oil producing sands will flow naturally for some period of time after they begin producing. Reservoir pressure and formation gas provide enough energy to bring fluid to the surface in a flowing well. As the well produces this energy is consumed and at some point there is no longer enough energy available to bring the fluid to the surface and the well will cease to flow. When the reservoir energy is too low for the well to flow, or the production rate desired is greater than the reservoir energy can deliver, it becomes necessary to put the well on some form of artificial lift to provide the energy to bring the fluid to the surface. One of the most used techniques for optimizing the oil and gas production systems, considering its verified effectiveness and world-wide level trustworthiness, is the Nodal Analysis (Beggs etal., 1991). In order to optimize the Production system using this technique, it is necessary describing the production system, making emphasis in the required energy balance between the reservoir and the installed Surface facilities, for establish the production capacity of the well. For this, it is necessary to construct a well model with reservoir and production variables. The Nodal Analysis allows to evaluate the p erformance of a completions of production, calculating the relation of the flow of production and the pressure drop that will happen in all the components, allowing to determine the flow of o il or gas that can produce a well bearing in mind the geometry of the perforation and increasing the rate of production to a low cost. In order to determine the Model of the System of Production using techniques of Nodal Analysis, it is necessary to describe the system of production, making emphasis in the balance of energy needed between the reservoir and the installed
Surface facilities; establish the capacity of production of the well, the variables of reservoir and of production, the correlations of flow selecting; and determine the properties of the fluids multiphase in the pipeline of production and the curve of gradient of pressure in the well corresponding to its real conditions of production (Beggs et al., 1991).
STATEMENT OF THE PROBLEM
Typical gas lifted wells have a stable behavior at elevated gas injection rates and unstable behavior at low gas injection rates. This means that a gas lifted well is not producing the maximum possible amount of oil at low gas injection rates in spite of the fact that these wells are operated most efficiently at these injection rates. Unstable operational conditions a re the most important reason for this. Operating a gas lifted well under un stable conditions has several disadvantages. First, the full lift potential in the gas is not properly used, resulting in a very inefficient operation. Second, surges in the production facilities may be so huge that severe operational conditions are likely to occur. Third, the static fluid level has fallen below the gas lift valve
PROJECT OBJECTIVES
The objective of this project is to develop a computerized model that will optimize production of various oil wells in X field. The method used here is the computerized approach using the Integrated production modeling (IPM) software packages which include the PROSPER (Production and Systems Performance analysis software. PROSPER can assist the production or reservoir engineer to predict tubing and pipeline hydraulics and temperatures with accuracy and speed. PROSPER's powerful sensitivity calculation features enable existing designs to be o ptimized and the effects of future changes in system parameters to be assessed. By separately modeling each component of the producing well system, then allowing the User to verify each model subsystem by performance matching, PROSPER ensures that the calculations are as accurate as possible. Once a system model has been tuned to real field data, PROSPER can be confidently used to model the well in different scenarios and to make forward predictions of reservoir pressure based on surface production data. MBAL, The material balance is based on the principle of conservation of mass: Mass of fluids
originally in place = fluids produced + remaining fluids in place The material balance pro gram uses a conceptual model of the reservoir to predict the reservoir behavior based on the effect of reservoir fluids production. GAP is a multiphase optimizer of the surface network which links with PROSPER and MBAL to model entire reservoir and production systems. GAP can model production systems containing oil, gas and condensate, in addition to gas or water injection systems.
GAP has the most powerful and fastest optimization engine in the industry. Wellhead chokes can be set, compressors and pumps optimized, and gas for gas lifted wells, allocated to maximize oil production or revenue while honoring constraints at any level. With MBAL, field production forecast can be run. PROJECT SIGNIFICANCE THE IPM CONCEPT
In its simplest form, the production system can be visualized as shown in the sketch below
The following elements needs to be considered when studying the behavior of the system
For a given reservoir how much of oil/gas is recovered at separator level depends on the facilities that connects the two Thus strategy is designed to maximize the oil and gas recovery Decision making process is based on how these components interact with each other.
This type of model is used to fulfill different objectives such as
Production allocation Short Term to Long Term forecasting
System Analysis Deliverability of a well can be severely restricted by the performance of only one component in the system. If the effect of each component on the total system performance can be isolated, the system performance can be optimized in more economic way. In system analysis we use a method where we consider whole production system as a single unit. Then we choose a point within the unit where input and output pressure is same. This is Nodal Analysis METHODOLOGY SUMMARY GAP, PROSPER, packages of IPM software will be used to model the different compone nt. The work flow intended is as stated below Optimization procedure Identify the components in the system • Select one component to be optimized • Select the node location that will best emphasize the effect of change • Develop expression for inflow and outflow • Calculate pressure drop versus rate for all components
• Determine the effect of changing the characteristics of the selecting component • Repeat the procedure for each component • Optimize the system
DETAILED PROSPER WORK FLOW
Sensitivity analysis will be carried out on the gas lift injection rate and pressure. PROJECT SIGNIFICANCE This project will discuss the manner in which to in terrelate the various pressure losses. In particular, the ability of the well to produce fluids will be interfaced with the ability of the piping system to take these fluids. The manner in which to treat the effect of the various components will be shown by a nodal concept. In order to solve the total producing system problem, nodes are placed to various portion defined by different equations or correlations.
The node is classified as a functional node when a pressure differential exists across it and the pressure or flow rate response can be represented by some mathematical or physical function. All of the components in the well, starting from the static pressure (Pr) and ending at the separator, are considered. This includes flow through the po rous medium, flow across the perforations and completion, flow up the tubing string with passage through a possible downhole restrict-on and safety valve, flow in the horizontal flow line with passage through a surface choke and on to the separator. Various positions and/or components are selected as nodes and the pressure losses are converged on that point from both directions. Nodes can be effectively selected to better show the effect of inflow ability, perforations, restrictions, Safety valves, surface chokes, tubing strings, flowlines and separator pressures. The appropriate multiphase flow correlations and equations for restrictions, chokes, etc. must be incorporated in the solution. In conclusion, an effective means of analyzing an existing well, making recommended changes or planning properly for a well can be accomplished by the nodal systems analysis. This procedure offers a means more economically optimize producing wells. CASE STUDY X field is located in the Eastern area of the onshore operational area. Field was discovered in 1975. Field has five major sands (AA-03, A-01, A-1.1, A-02 and B-01).First production in 197 9. AA03 Reservoir constitutes about 70% of the total HC . Field has
16 HC reservoirs 5 active / 2 inactive Producers 8 wells drilled to date
Average Production has declined from 12,000 BOPD in October 1993 to about 5,300 BOPD currently. FIELD SPECIFICS 6P STOOIP
150 MMBO
Cumulative Production (06/2011)
46 MMBO
Cum Gas Production (06/2011)
36.7 Bcf
Oil Reservoirs
5
Gas Reservoirs
6
Average Production Depth
6,500ft
Average API Gravity
34.4
Average Porosity, Water Saturation
~24%