Process Control Philosophy

VIETSOVPETRO - VIETNAM

NAM RONG – DOI MOI RC-4 Wellhead Platform

PROCESS CONTROL PHILOSOPHY

A

18.11.08

ISSUED FOR CLIENT'S COMMENTS

RM

VJ

AMA

REV.

DATE

DESCRIPTION

PRPD.

CHKD.

APPD.

TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE

Saipem Triune Engineering Pvt. Ltd., New Delhi

PROCESS CONTROL PHILOSOPHY

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TABLE OF CONTENTS

1

INTRODUCTION………………………………………………………………………..4 1.1

OBJECTIVE……………………………………………………………………...4

2

GENERAL DESCRIPTION ……………………………………………………………4

3

ABBREVIATIONS………………………………………………………………………5

4

BRIEF PROCESS DESCRIPTIONS……………………………………………..……...6

5

DESIGN BASIS………………………………………………………………………….8

6

5.1

DESIGN FLOW RATES………………………………………….……………..8

5.2

OPERATING & DESIGN CONDITIONS………………………………………9

5.3

COMPOSITION OF CRUDE OIL FEED……………………………………....10

5.4

COMPOSITION OF GASLIFT GAS……………………………………….…..11

5.5

CHARECTERISTICS OF PSEUDO COMPONENTS…………………………12

5.6

METEROROLOGICAL DATA……………………………………………..….13

5.7

SIMULATION CASES……………………………………………………..….14

PROCESS SYSTEM CONTROL PHILOSOPHY………………………………………21 6.1

FACILITIES TO CONTROL …………………………………………………...21

6.2

TYPES OF BASIC CONTROL ………………………………………………...22

6.3

BRIEF DESCRIPTION OF MAIN CONTROL SYSTEMS …………………...23 3.1

PROCESS CONTRO & MONITORING SYSTEM (PCS)……………..23

3.2

SAFETY & EMERGENCY SHUTDOWN SYSTEM (SSD)…………..25

6.3.3

FIRE & GAS DETECTION & FIRE FIGHTING (FGS)……………....26

6.3.4

REDUNDANT LOCAL AREA NETWORK (R-LAN)……………..…27

6.3.5

SCADA……………………………………………………………….…28

6.3.6

WELLHEAD CONTROL PANEL (WCP) …………………………….28

TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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7

OPERATION AND CONTROL OF PROCESS SYSTEMS……………….…………..29 7.1

WELL FLOW LINES CONTROL…………………………..………………29

7.2

INLET MANIFOLD CONTROL……………………………………………31

7.3

TEST METERING STATION………………………………………………32

7.4

RISERS CONTROL…………………………………………………………32

7.5

PRODUCTION SEPERATOR V-400………………………………………33

7.6

7.7

7.8

7.9

7.5.1

SEPARATOR LEVEL CONTROL……………………………….34

7.5.2

SEPARATOR PRESSURE CONTROL……………………….….35

7.5.3

CUSTODY FLOW METERS……………………………………..36

7.5.4

SEPARATOR OTHER CONTROL……………………………….36

VENT SCRUBBER V-200…………………………………………………..37 7.6.1

VENT SCRUBBER TEMPERATURE CONTROL………………37

7.6.2

VENT SCRUBBER LEVEL CONTROL …………………………37

CLOSE DRAIN & OPEN DRAIN SYSTEM (V-300 & V-301)……………38 7.7.1

DRAIN TANKS TEMPERATURE CONTROL…………………..39

7.7.2

DRAIN TANKS LEVEL CONTROL……………………………..39

GASLIFT DISTRIBUTION SYSTEM………………………………………40 7.8.1

GASLIFT METERING STATION………………………………..40

7.8.2

GASLIFT GAS TO INDIVIDUAL WELL………………………..41

7.8.3

GASLIFT FOR SLUG REMOVAL & FOR GAS DISPOSAL…...42

CHEMICAL INJECTION SYSTEM………………………………………..43 7.9.1 7.9.2

DEPRESSANT…………………………………………………..43 DEMULSIFIER………………………………………………….44


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1.INTRODUCTION 1.1

OBJECTIVE The purpose of this document is to define the main control functions for the process system. It is intended that this document be used for the following. •

Developing and/or reviewing P&ID’s.

•

Guidance to control engineer in developing the instrument hardware requirements

•

In developing Operating Procedures, Operating Manuals, etc.

2.GENERAL DESCRIPTION Well fluids from DRAGON Oilfield located in the Continental Shelf of South Vietnam, shell be collected at RC4 Platform which is owned by VIETSOPETRO, a Joint venture of Vietnam & Soviet. The RC-4 Platform comprises of the following process facilities : •

Collection of well fluid from various Wells: Wells number 01 to 09.

•

3 Injection Wells where Injection water is used.

•

Separation of Gas & liquid and transportation of gas & liquid to the Processing platforms RP-1, RP-2 & RP-3.

•

Gas Lift disposal to cold vent through Vent Scrubber.

•

Gaslift Distribution System.

•

Risers balcony where Gas & Liquid from other platforms RC-5 & RC-DM are also joining.

•

Risers for Gaslift from RP-3 platform and distributing to other platforms. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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3.ABBREVIATIONS API APS AS CCR DCTS DCU DTU EDG ESD F&G HV HVAC LCP LCS MCC MCC P&ID PA / GA PCS PGCS PLC PSD PSMCS RB SCADA SCSSV SWP UPS USD WCP WS

American Petroleum Institute Platform Abandonment Signal Area Supervisory Station Central Control Room Data Collection and Transfer System Data Collection Unit Data Transfer Unit Emergency Diesel Generator Emergency Shutdown Fire and Gas High Voltage Heating Ventilation and Air Conditioning Local Control Panel Local Control System Motor Control Centre Motor Control Centre Piping and Instrumentation diagram Public Address / General Alarm System Process Control System Power Generation Control System Programmable Logic Control Process Shutdown Power Supply Monitoring and Control System Riser Block / Balcony Supervisory Control and Data Acquisition Surface Controlled Subsurface Safety Valve Satellite Well Platform Un-interruptible Power Supply Unit Shutdown Wellhead Control panel Work Station


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4.BRIEF PROCESS DESCRIPTION

The crude oil from all 9-production wells reaches to inlet manifold skid of RC-4 via their own respective flow lines. The manifold skid is assigned for collection and distribution of well product into individual process lines. It consists of blowdown valves and 4 headers as below. a) Well production Collection Header b) Testing Header for well testing and metering c) Vent Header d) Drain Header Fluid from wellhead passes through a choke valve to control the flow towards production header. From production header, well fluid is routed to Inlet separator which is a two phase separator or it is directly routed to remote processing platform RP-3 through sub sea pipeline by bypassing the inlet separator. Separated liquid/gas mixture from separator after level control valve is transported to RP-1 via sub sea pipe line. The Pig Launcher is also provided at RC-4 platform on this line. Liquid/gas mixture from platform RC-DM is also routed to RP-1 platform via RC-4 through RC-4 liquid/gas mixture line. There is a Pig receiver at RC-4 platform on the RC-DM liquid/gas mixture line. Test header after the Test Metering Station is also routed to separated liquid/gas mixture line after Production Separator level control valve. The Produced Gas from Production Separator after its pressure control valve is transported to RP-3 platform through a common gas transferring line. There are two more similar facility TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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platforms RC-5 & RC-DM at the same area whose gas production goes to RP-3 platform via RC-4 platform through this common gas line to RP-3. The Gaslift gas from processing platform RP-3 arrives at RC-4 platform via 16 Km long pipeline. After reaching at RC-4 platform, it is divided into three lines for RC-4, RC-5 & RCDM platform use. 8” Gaslift line towards RC-4 is reduced to 4” and then goes to a metering station. From metering station, gaslift gas is distributed to all 9-production wells through gaslift distribution manifold by flow controller. The discharge of all PSVs, BDVs from manifold, Production Separator & Gaslift distribution system is routed to Vent Scrubber via vent header. The gaseous discharge form Vent Scrubber is sent to Vent Stack through liquid seal. The liquid discharge from Vent Scrubber is collected in Close drain Tank. The drip pan liquid collected from all equipments and inlet manifold skid is routed to Open Drain Tank. The combined discharge from Closed & Open Drain Tank has provision to transfer the material to liquid/gas mixture line through a drain pump or directly to disposal sump or to support vessel as produced water accordingly. Water Injection line from RP-3 arrives at RC-4 platform. After reaching at RC-4 platform Riser balcony, it is divided into three lines for RC-4, RC-5 & RC-DM platform use. RC-4 water injection line shall go to three injection wells. A tapping is taken from this header for Killing manifold which is required for 9 production wells & 3 Injection Wells at RC-4 platform. Demulsifier and Depressant Chemicals storage and injection facility are installed on the platform.


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5.DESIGN BASIS

5.1. DESIGN FLOW RATES

Production Wells

9

Injection Well

3

Liquid production

6000 Tonns/day

Oil

5500 Tonns/day

Water

500 Tonns/day

Maximum liquid per well

1200 Tonns/day

Maximum Gaslift gas for all wells

400,000 NM3/Day

Gaslift gas per Well Maximum Injectivity of an injection

10000 - 50000 NM3/Day

well

Upto 1000 m3/day

Notes: 1.

Liquid production of 6000 Tonnes/day is the total maximum design liquid capacity for all 9 wells together.

2.

Inlet production Separator Gas capacity shall be “400,000 NM3/day + Associated gas with the crude oil based on Hysys calculation”.


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5.2. OPERATING AND DESIGN CONDITIONS

PRESSURE

TEMPERATURE

Operating

Design

Operating

Design

Bar g

Bar g

°C

°C

Production Header

16-41

80

55

60

Test Header

16-41

80

55

60

Vent Header

2

11.5

55

-48 / 60

Drain Header

ATM

11.5

55

60

105-110

125

22-30

45

16-41

60

55

60

2

11.5

55

-48 / 60

16-41

80

55

60

Close Drain Tank

0.7

5.8

55

60

Open Drain Tank

ATM

3.5

55

60

Gaslift gas Production Separator Vent Scrubber Pig Launcher/Pig Receiver

5.3. COMPOSITION OF CRUDE OIL FEED TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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Component

Unit

Quantity

N2+RARE

Mole %

0.068

CO2

Mole %

0.038

H2S

Mole %

0

CH4

Mole %

12.308

C2H6

Mole %

3.099

C3H8

Mole %

6.023

i-C4H10

Mole %

1.52

n-C4H10

Mole %

3.141

i-C5H12

Mole %

3.901

n-C5H12

Mole %

5.409

Pseudo C6

Mole %

6.766

Pseudo C7+

Mole %

57.727

Mol. Wt.

g/mole

227.8


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5.4. COMPOSITION OF GASLIFT GAS

Component

Unit

Quantity

N2+RARE

Mole %

0.175

CO2

Mole %

0.068

H2S

Mole %

0

CH4

Mole %

73.622

C2H6

Mole %

12.992

C3H8

Mole %

7.635

i-C4H10

Mole %

1.643

n-C4H10

Mole %

2.358

i-C5H12

Mole %

0.591

n-C5H12

Mole %

0.64

Pseudo C6

Mole %

0.406

Pseudo C7+

Mole %

0.119

Pseudo C8+

Mole %

0.02

Relative density Mol. Weight

0.784 g/mole


22.75

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5.5. CHARACTERISTICS OF PSEUDO COMPONENTS

IN CRUDE OIL Pseudo C6

Normal Boiling Point (NBP) 66 °C

Pseudo C7+

Molecular Weight 86 358.8

Std. Ideal Liquid Density 663 kg/m3 at 20 °C 861 - 903.9 kg/m3 at 20 °C Average density 875 kg/m3

IN GASLIFT Pseudo C6

Normal Boiling Point (NBP) 66 °C

Molecular Weight 86

663 kg/m3 at 20 °C

Pseudo C7+

96 °C

100.2

683 kg/m3 at 20 °C

Pseudo C8+

124 °C

114.2

702 kg/m3 at 20 °C


Std. Ideal Liquid Density

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5.6. METEOROLOGICAL DATA Climate

: Salten Offshore Tropical

Max Wind Speed

: 57.4 m/sec

Normal Wind Speed

: 8.7 m/sec

Min, Wind Speed

: 0.0 m/sec

Barometric Pressure

: 996 – 1022.2 mbar

Ambient Air Quality Maximum temperature outdoor air

: 41 °C

Minimum temperature outdoor air

: 21 °C

Normal temperature outdoor air

: 35 °C

Dry bulb temperature

: 27 0F

Relative Humidity of outdoor air

: Maximum 100% to Minimum 56%

(-2.8 °C) Minimum

Miscellaneous : Solar Radiation

: 335 kcal/ m2hr

Sea Water Temperature

: 24.12 °C – 34.59 °C

Sea water Salinity

: 293 - 3459 mg/l

Sea water Density

: 1018.4 - 1024.19 Kg/M3

Seismic Conditions Maximum Seismicity

: 6 Richter Scale .

5.7. SIMULATION CASES TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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The simulation is carried out to know the process conditions at various possible cases based on operating pressure & properties of crude oil system & the gas lift system.

Case 1 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day

Production Separator Operating Pressure

16 Barg

Gas Lift Operating Temperature

30 °C

Gas Lift Operating Pressure

105 Barg

Case 2 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


41 Barg


30 °C


105 Barg

Case 3 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


16 Barg


30 °C


110 Barg


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Case 4 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


41 Barg


30 °C


110 Barg

Case 5 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


16 Barg


22 °C


105 Barg

Case 6 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


41 Barg


22 °C


105 Barg

Case 7 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


16 Barg


22 °C


110 Barg


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Case 8 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


41 Barg


22 °C


110 Barg

Case 9 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


16 Barg


30 °C


105 Barg

Case 10 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


41 Barg


30 °C


105 Barg

Case 11 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


16 Barg


30 °C


110 Barg


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Case 12 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


41 Barg


30 °C


110 Barg

Case 13 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


16 Barg


22 °C


105 Barg

Case 14 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


41 Barg


22 °C


105 Barg

Case 15 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


16 Barg


22 °C


110 Barg


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Case 16 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


41 Barg


22 °C


110 Barg

Case 17 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


30 Barg


30 °C


105 Barg

Case 18 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


30 Barg


30 °C


105 Barg

Case 19 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


30 Barg


30 °C


110 Barg


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Case 20 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


30 Barg


30 °C


110 Barg

Case 21 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


30 Barg


22 °C


105 Barg

Case 22 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


30 Barg


22 °C


105 Barg

Case 23 : Oil

5500 Tonns/ Day

Water

500 Tonns/ Day


30 Barg


22 °C


110 Barg


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Case 24 : Oil

6000 Tonns/ Day

Water

0 Tonns/ Day


30 Barg


22 °C


110 Barg

The above simulation cases have been utilized for preparation of PFD, Heat and Material Balance, data-sheets and other engineering documents. The equipment & pipelines are sized according to the governing cases out of above twenty four different cases.


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6.PROCESS SYSTEM CONTROL PHILOSOPHY

6.1

FACILITIES TO CONTROL

The philosophy of automation, monitoring process control system, safety instrumented system & hazard-monitoring system is prepared for RC-4 platform following facilities.

•

Production Wells control through Wellhead Control Panel

•

Injection Wells control

•

Process Equipments

•

Power generation control

•

Auxiliary Equipments

•

Fire Fighting Facility

•

Emergency handling

•

Accommodation platform control system


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6.2

TYPES OF BASIC CONTROL

The basic control system of RC-4 Wellhead Satellite platform is through PCS & PLC and it is operated from the Control Room Workstation at RC-4 platform. The monitoring & control systems of RC-4 Platform are being done through following systems:

•

Process Control System (PCS)

•

Safety & Emergency Shutdown System (SSD)

•

Fire & Gas System RC4 (FGS)

•

Redundant Local Area Network (R-LAN)

•

SCADA

•

Radio Equipment

•

24 VDC Uninterrupted Power Supply systems for monitoring, control & safety facility including PA/GA & Radio Equipment.

•

PA/GA System

•

Data Collection Interface (DCI)

•

Work-Station PCS/ SSD/ FGS – (WS-1)

•

Wellhead Control Panel (WCP)

•

Navigation System Panel


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6.3

BRIEF DESCRIPTION OF MAIN CONTROL SYSTEMS

The following control levels should be provided. •

Level – 0 :

Field sensors & execution system

•

Level – 1 :

Hardware at the PLC basis (central panel : PCS, SSD, FGS)

•

Level – 2 :

SCADA at RC4 (Software & hardware for supervisory control & data acquisition)

6.3.1

PROCESS CONTROL AND MONITORING SYSTEM (PCS):

PCS should do the normal control and monitoring of the process parameter. Moreover PCS at RC4 platform is having facility to provide safety of personnel, environment, equipment and platform as a whole. PCS shall be in RC4 Platform Control Room and should have following minimum control.

•

Control of Oil & Gas Production, Processing & transportation.

•

Control of Main & auxiliary process equipments.

•

Interface with Well Test Unit and Metering Unit.

•

Control & Monitoring Power Supply System. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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The PCS should serve minimum following functions.

a) Provide graphical display of process information for monitoring and interacting with facility process equipment. b) Displaying, managing & archiving the alarms and events from all systems. c) Continuous recording of process data in historical archive files. d) Graphical trending of both real time and historical data. e) Generate production data reports. f) Interfacing to third-party vendor systems. g) Provide master communication protocol between all subsystems. h) PCS shall carry out functions of self–diagnostics and internal malfunction alarm. i) PCS shall be tested without process shutdown in case of change of software or loading of new software. j) PCS will have hardware panels for visual indication of critical alarms, Critical Valves status and Critical control switches.

Notes: 1. PCS shall be provided with 100% redundancy to take care of failure condition of Central Processor (CPU). Both the CPU should have same control computation program in synchronization so that changeover can be done without any interruption. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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6.3.2

SAFETY & EMERGENCY SHUTDOWN SYSTEM (SSD):

The main purpose of SSD should be to provide following as a minimum. •

Safety of staff, environment and process equipment of WHP RC-4 as a whole.

•

Automatic emergency shutdown of processes and equipment by critical parameters and also send indispensable signals to other systems.

•

Provide remote diagnostic calibration and testing.

•

Provide functions of self-diagnosis and signaling about internal faults with automatic registration and printing.

SSD shell be comprising of followings. •

ESD-A (Emergency Shutdown – Abandon Platform)

•

ESD-C (Shutdown due to emergency on other platforms)

•

PSD (Process Shutdown)

•

PSD-GL (Process Shutdown – Gaslift)

•

ESD-GL (Emergency Shutdown – Gaslift)

•

Receiving signal from FGS Panel for ESD-F & ESD-G.

The system SSD includes the equipment of following levels: •

Level 0 : Field sensors of critical parameters and execution units of emergency shutdown. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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• 3.3

Level 1 : SSD-Panel (hardware on the PLC basis).

FIRE & GAS Detection and Fire Fighting Control System at RC-4 (FGS) :

Fire and gas detection and fire-fighting control system (FGS) is a separate dedicated system and F&G Panel should be installed in RC-4 control room and have autonomous standby power supply unit. The main purpose of Fire & Gas control panel should be to provide following as a minimum. •

Safety of staff, environment and process equipment of WHP RC-4 as a whole.

•

Automatic detection of the location of the Fire through UV/ IR flame detectors system, fusible loop and location of the HC gas leak at the different location on the different decks of the RC4 platform.

•

The FGS shall act upon receiving indication from detectors & manual shutdown push buttons to generate the Emergency Shutdown ESD-F or/and ESD-G signals accordingly and transfer the critical signals to the SSD and to the other systems.

•

Automatic Control on RC-4 Fire Fighting System.

The system FGS includes the equipments of the following levels: •

Level 0 : F&G field detectors, actuators of RC-4 fire-fighting systems.

•

Level 1 : FGS-Panel (hardware at PLC base).


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FGS shall provide the following levels of shut down according to level of danger for personnel, environment, process equipment, and platform as a whole.

ESD-F : Emergency shutdown and process blow-down for personnel safety and equipment/ unit safety. Furthermore APS push buttons for activation of ESD signals to abandon platform shall be provided. ESD-G: Emergency shutdown and bringing technological processes and equipment in safe condition but without pressure blowdown except to release high pressure Gaslift system.

The F & G system at RC4 shall cover only RC-4 platform. Control system shall execute auto and remote control of systems and devices for extinguishing of fire at RC-4 (Fire fighting system – fire water pump, fire monitor, fire sprinkler, foam system, CO2 etc) as well as switching off the HVAC system.

3.4

REDUNDANT LOCAL AREA NETWORK (R-LAN): •

Local Information Network should have connection with PCS & PLC (SSD) through necessary software and external interfaces.

•

Local Area network (R-LAN) shall transfer the information from PCS to SCADA.

•

Information by Radio Channel should transfer through R-LAN. It includes ESD-C information to / from processing platform RP-3 & RP-1. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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3.5

SCADA (Supervisory Control and Data Acquisition)

SCADA should provide receiving / transferring, processing, registration, storage and visual display of the information on workstations from/to systems PCS, SSD, FGS and receiving / transferring of the necessary information through DCI by the radio channel. It should be provided with ability to retrieve from archive the basic process parameters (PT/TT - of each separate well, PT / TT / LT - of process equipment), Well Test Unit and Metering Unit with indication in WS-1, demonstrating parameters variation diagrams of each separate well and technological process for a certain time or for all period of data storage. SCADA should provide warning signaling (as the controlled process parameters over set points) and alarm signaling (in emergencies) - light and sound signaling at workstation (WS-1).

3.6

Wellhead Control Panel (WCP):

WCP- should provide with the following remote controls from the system SSD: a) Shutdown of separate wells (PSD-Closed WSSV, PSD-Closed MSSV) - automatically from the process control instruments or manually by the command of operator – technologist from workstation WS-1; a) Shutdown of all wells (ESD-Closed all WSSV / MSSV / SCSSV) - automatically from the control instruments/systems or manually by the ESD command of operator – technologist from workstation WS-1


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SHEET 31 OF 48

7

OPERATION AND CONTROL OF PROCESS SYSTEMS

Description of the operation and control of the process is divided into different sections as below.

7.1

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Well Flow lines

•

Inlet Manifold

•

Test Metering Station

•

Risers

•

Production Separator

•

Vent Scrubber

•

Open & Close Drain system

•

Gaslift Distribution system

•

Chemicals Injection

Well Flow lines Control

There are nine separate wells with wellheads and flow lines at the RC-4 Wellhead platform. The wellhead of every well is consists of the following main instrumentations. For isolating a Well, there is underwater Sub Surface Safety Valve (SCSSV) and One master & One wing valve on the wellhead. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY Saipem Triune Engineering Pvt. Ltd., New Delhi

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Master Surface Safety valves (RC4-MSSV-0011/ 0021/ 0031/ 0041/ 0051/ 0061/ 0071/ 0081/ 0091).

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Wing Surface safety valves (RC4-WWSSV 0011/ 0021/ 0031/ 0041/ 0051/ 0061/ 0071/ 0081/ 0091).

•

Positive Flow chock Valves (RC4-FV-0011/ 0021/ 0031/ 0041/ 0051/ 0061/ 0071/ 0081/ 0091).

•

The chock valves are hydraulically actuated step by step. Choke valve shall close only after wing valve closes (upon LSD or manual initiation), Choke valve closing time is adjustable. Reopening of choke valve is only possible only when wing valve is fully open.

The low & high pressure switches are provided on each well flow line after the Chock valves. The tag numbers are RC4-PSHL 0011/ 0021/ 0031/ 0041/ 0051/ 0061/ 0071/ 0081/ 0091 respectively. PSHL will create electrical signal at high pressure of 50 barg & low pressure of 10 barg, which goes to Well Head Control Panel (WHCP) to shutdown the individual Well. Each flow line is protected against high pressure by providing a Shutdown valve SDV (RC4SDV-0011/ 0021/ 0031/ 0041/ 0051/ 0061/ 0071/ 0081/ 0091 respectively for 9 wells) followed by three pressure transmitters, which shall be used for shutdown purpose. On actual high pressure in the individual flow lines, the indication from these three pressure transmitters shall generate Pressure High High alarm signals in PLC and based on the “2 out of 3” voting system, PLC shall activate the Pressure High High interlock (RC4-PAHH-1011/ 1021/ 1031/ 1041/ 1051/ 1061/ 1071/1081/ 1091 respectively for 9 production wells) which shall shutdown the SDV in flow line and other appropriate shutdown of the system. (For detail , see the Cause & Effect Matrix)


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Each well flow line is having a check valve and a safety valve. The operating temperature of each flow line is 55 degC and the operating pressure range is from 16 to 41 barg.

7.2

Inlet manifold Control Inlet manifold is having four headers, Production Header, Test Header, Vent Header & Drain Header. The production Header is designed to receive the crude oil from all the flow lines together. Production Header is provided with local pressure & temperature gauges and a pressure transmitter with Low & High pressure alarms on PCS. To release the pressure of production header, blowdown valve RC4-BDV-1001 is provided to depressurize it, which operate automatically on ESD. A Test header is provided at the Inlet manifold which allows testing of each well separately. To release the pressure of test header, blowdown valve RC4-BDV-1002 is provided, which operate automatically on ESD. The operating pressure of these headers is 16-41 barg & operating temperature is 55 degC.


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7.3

Test Metering Station As such there is no control on the test metering station. Whenever a well is to be tested for it’s components, that flow line is to be lined-up to the test header. From test header, flow is routed to the metering station. On metering station, a Multi Phase Flow devise is provided which shall indicate the flow rate of Gas, Oil & Water in the crude oil stream.

7.4

RISERS CONTROL All the platforms (RC-4, RC-5, RC-DM, RP-1, RP-2, RP-3) produced gas, mixture of oil & gas, Gaslift gas & water injection are interconnected through risers. Produced gas from RC-5 (Riser-06) & RC-DM (Riser-07) are coming to RC-4 platform & from here altogether with RC-4 Produced Gas, these are transferred to RP-3 / RP-2 platform through Riser-08. Mixture of oil & gas from RC-DM (Riser-05) is coming to RC-4 platform & from here altogether with RC-4 they are transferred via Riser –04 to RP-1 through RC-5 platform. Gaslift gas from RP-3 (Riser-02) is coming to RC-4 platform & from here it is getting distributed to RC-DM (Riser-03), RC-5 (Riser-01) & RC-4 usage. Water for injection is coming from RP-3 (Riser-09) on RC-4 platform & from here it is getting distributed to RC-4, RC-5 (Riser-10) & RC-DM (Riser-11). TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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Shutdown Valves SDVs are provided on the Risers where service is Hydrocarbon fluids. Hand Operated valves are provided in water injection line with limit switches to know the open & close status of these hand valves on Risers. In case of emergency on Risers, low low pressure & high high pressure on Produced Gas & Liquid Risers and only low low pressure on Gaslift Risers are provided to shutdown the respective SDV and other related SDV accordingly. (For detail , see the Cause & Effect Matrix)

7.5

PRODUCTION SEPARATOR V-400 : Crude Oil from Production header enters into the Production Separator. The operating pressure of at 16-41 barg and 55°C. Production Separator is a 2 phase Horizontal separator to separate well fluid into gas & liquid phase. Liquid, containing oil & water, is collected in bottom and provided to stay in the separator for some predetermined time based on the load to disengage the trapped gases before going out from separator bottom. Produced gas from separator overhead under separator pressure control is transferred to processing platform RP-3 while the produced liquid from separator bottom under level control is transferred to processing platform RP-1 via RC-5 platform.


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7.5.1

PRODUCTION SEPARATOR LEVEL CONTROL: Production separator liquid level is monitored and controlled by Interface level controller RC4-LIC-400 on auto mode by operating level control valve RC4-LCV-400, which is located at separator bottom outlet liquid line. Level controller gets the indication from local level transmitter RC4-LT-400 that is installed on standpipe of production separator. It keeps a watch on interface level and hence relative liquid residence time in the separator to ensure effective separation. NOTE: 1. On level transmitter failure, its indication should show bad value with alarm and level controller should be forced automatically to go on Manual mode from Auto mode, leaving Level Control valve at its last output position. 2. Above action shall give the warning alarm to operation personnel but considering the normal steady rate, unnecessary shutdown can be avoided.

Another level transmitter RC4-LTS-401 is provided on separator to keep watch on it’s very low and very high level and during such condition, this transmitter signal to PLC generate Low-Low level alarms or High-high level alarms to take proper action through PLC. (For detail , see the Cause & Effect Matrix) However, as same level control valve RC4-LCV-400 is to get trip through PLC in case of low low level in separator so proper instrumentation system is required for the operation of this valve during normal and emergency.


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7.5.2

PRODUCTION SEPARATOR PRESSURE CONTROL: Production separator pressure is monitored and controlled by Interface pressure controller RC4-PIC-400 on auto mode by operating pressure control valve RC4-PCV-400, which is located at separator overhead outlet gas line. Pressure controller gets the indication from local pressure transmitter RC4-PT-400. Depending on the operating scenarios between the other platform, it’s set point is to be decided which can vary from 16 barg to 41 barg. NOTE: 3. On pressure transmitter failure, its indication should show bad value with alarm and pressure controller should be forced automatically to go on Manual mode from Auto mode, leaving pressure Control valve at its last output position. 4. Above action shall give the warning alarm to operation personnel but considering the normal steady rate, unnecessary shutdown can be avoided.

Another pressure transmitter RC4-PTS-402 is provided on separator to keep watch on it’s very low and very high pressure and during such condition, this transmitter signal to PLC generate Low-Low pressure alarms or High-high pressure alarms to take proper action through PLC. (For detail , see the Cause & Effect Matrix) However, as same pressure control valve RC4-PCV-400 is to get trip through PLC in case of low low pressure in separator so proper instrumentation system is required for the operation of this valve during normal and emergency.


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7.5.3

CUSTODY FLOW METERS Custody flow meter RC4-FT-401 is provided in outlet gas line from separator. Being a custody meter, proper pressure and temperature compensation is provided on Gas Flow meter by pressure transmitter RC4-PT-401 & RC4-TT-401. The compensated flow is indicated by RC4FI-401 on PCS and the Cumulative flow is indicated by RC4-FQI-401 on PCS. Custody flow meter RC4-FT-402 is provided in outlet liquid line from separator. RC4- FI-402 indicates the flow on PCS and the Cumulative flow is indicated by RC4-FQI-402 on PCS.

7.5.4

OTHER MONITORING & CONTROL IN PRODUCTION SEPARATOR a)Gas outlet demister pad differential pressure transmitter is provided to know about the chocking in the demister pad. b)Temperature transmitter RC4-TT-402 is provided in liquid phase and its indication RC4-TI402 is provided on PCS. c)Blow-down facility is provided to reduce pressure in the separator in case of fire or other emergencies.


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SHEET 39 OF 48

7.6

VENT SCRUBBER V-200: The vent scrubber separates hydrocarbon liquid carried over by the gas in the vent header. The knocked out vapor goes to vent tip while the accumulated liquid is transferred to closed drain tank V-301 by gravity. There is provision to empty out the scrubber through Drain pump.

7.6.1

VENT SCRUBBER TEMPERATURE CONTROL : During emergency release of gas & liquid from process system, there is potential of low temperature discharge in the vent header & vent scrubber. An immersion electric heater RC4HT-200 is provided in the Vent Scrubber in liquid phase, which is operated to control the vent scrubber liquid phase temperature to avoid congealing of the oil. A temperature switch RC4TSH-200 is provided in the liquid phase to control the ON / OFF power to the heater. In normal operation while no liquid is there, this heater should remain OFF. The normal operating temperature in the system is 55 degC but the set point of TSH can be kept much below 55 degC, depending upon the characteristic of the crude in the vent & drain headers. There is a temperature transmitter RC4-TT-200 in liquid phase whose indication RC4TI-200 comes on PCS with high and low alarms on PCS.

7.6.2

VENT SCRUBBER LEVEL CONTROL : In normal operation, as such there is no level control on vent scrubber. But during any emergency discharge, during draining of a system or due to any upset, the level can go up. So to avoid liquid to go into the scrubber overhead vent, a high high level protection is provided. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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Level transmitter RC4-LT-200 on the scrubber shall provide the level indication to PCS with low & high alarms. Same LT indication is also going to PLC and during very high level, RC4LAHH-200 shall initiate the PSD interlock to take the shutdown of the process shutdown. During low low level, signal RC4-LALL-200 shall come to the soft selector switch RC4-SS300 which is located on PCS and if the vent scrubber is selected for drain pump, then RC4LALL-200 shall activate USD via RC4-SS-300 which shall send signal to MCC to stop motor of drain pump RC4-H-311.

7.7

CLOSE DRAIN & OPEN DRAIN SYSTEM: Overall Drain system consists of Open drain header, closed drain header, Closed drain tank (V301), Open drain tank (V-300) and a common reciprocating drain pump RC4-H-311. Close drain tank is receiving the liquid from closed drain header where equipment draining is lined up. Vent Scrubber can also be drained into the Close drain tank. In normal operation, there is no such draining. The open drain tank receives flow from all drip pans liquid collected from all equipments & inlet manifold skid. Generally this header is not a pressurized header and should be self-drain towards the open drain tank. Vapours from V-300 & V-301 are vented to atmosphere via flame arrestor. The HC liquid is transferred by drain pump RC4-H-311 to mixture of oil & gas liquid line to RP-1. During maintenance, whatever the liquid is collected in the Drain Tanks, that can be send to disposal system or produced water to support vessel accordingly. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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SHEET 41 OF 48

7.7.1

OPEN DRAIN & CLOSED DRAIN TANK TEMPERATURE CONTROL: During emergency release of gas & liquid from process system, there is potential of low temperature discharge in the vent header & vent scrubber. Vent scrubber can be drained into the closed drain tank or liquid can come to the tank directly from the drain header. An electric heater RC4-HT-301 is provided in the Close Drain Tank in liquid phase, which is operated to control the tank liquid phase temperature. A temperature switch RC4-TSH-301 is provided in the liquid phase to control the ON / OFF power to the heater. In normal operation while no liquid is there, this heater should remain OFF. The normal operating temperature in the system is 55 degC but the set point of TSH can be kept much below 55 degC, depending upon the characteristic of the crude in the vent & drain headers. Local temperature gauge RC4-TG-301 is provided on the close drain tank in the liquid phase.

7.7.2

OPEN DRAIN & CLOSED DRAIN TANK LEVEL CONTROL: In normal operation, as such there is no level control on both the tank. But during any emergency discharge, during draining of a system or due to any upset or vessels maintenance drain, the level can go up. So to avoid liquid to go into the overhead vent, an overflow line is provided on both the vessels. But for low level protection, level transmitter RC4-LT-300 & RC4-LT-301 are provided respectively on open & close drain.


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SHEET 42 OF 48

During low low level, signal RC4-LALL-300 OR RC4-LALL-301 shall come to the soft selector switch RC4-SS-300 that is located on PCS. According to the selection of the equipment Level in selector switch, the interlock shall initiate to activate USD via RC4-SS300. USD shall send signal to MCC to stop motor of drain pump RC4-H-311.

7.8

GASLIFT DISTRIBUTION SYSTEM

7.8.1

GASLIFT METERING STATION Gaslift gas line of 8”, coming from processing platform RP-3 through RISER-02, is reduced to 4” followed by a Shutdown Valve RC4-SDV-800 and Gaslift metering station. Transmitter RC4-FT-801 monitors Gaslift gas flow towards RC4. The flow device is Simplex change type orifice fitting with four bored plates, one per range. As the requirement of Gaslift in the well can vary from minimum required to maximum so to cover the wide range of flow rates with accuracy, Gas metering station shall provide three flow ranges for which three different bore size orifice plates are to be kept ready to install in the orifice fittings as required. Based on the design capacity of Gaslift system and the minimum requirement of Gaslift to one well, the range of these orifices is to be decided during detailed engineering. The flow transmitter indication RC4-FI-801A shall display on PCS. Pressure Transmitter RC4PT-802 & Temperature Transmitter RC4-TT-801 are provided for pressure & temperature compensation to the gaslift flow. The compensated flow is indicated by RC4-FI-801 and the cumulative flow is indicated by RC4-FQI-801 on PCS.


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SHEET 43 OF 48

In emergency on platform or on the gaslift metering station, a blowdown vlave RC4-BDV-801 is provided to release the pressure.

7.8.2

GASLIFT GAS TO INDIVIDUAL WELL Gaslift from metering station shall go to the gas distribution manifold where gas is distributed to all wells. Gaslift flow is being controlled towards each well through an angle valve with diaphragm actuator (RC4-FCV-811/ 812/ 813/ 814/ 815/ 816/ 817/ 818/ 819 respectively for 9 wells). Flow is being monitored by flow transmitters RC4-FT-811/ 812/ 813/ 814/ 815/ 816/ 817/ 818/ 819 respectively for 9 wells). The individual flow device is Simplex change type orifice fitting with four bored plates, one per range. The requirement of Gaslift in the well can vary from minimum required to maximum or even intermittent use of gaslift, depending on the oil capacity in the wells. To cover the wide range of flow rates with accuracy, each line is be provided with four flow ranges for which four different bore size orifice plates are to be kept ready to install in the orifice fittings as required by mode of operation. Based on the design capacity of Gaslift system and the minimum requirement of Gaslift to one well, the range of these orifices is to be decided during detailed engineering. A selector switch is provided on PCS for selecting “Installed Bore” size which shall be the input to the PLC base controller RC4-FY-811/ 812/ 813/ 814/ 815/ 816/ 817/ 818/ 819 respectively for 9 wells. The PLC based logic shall work according to wide range of gaslift requirement & header pressure. Accordingly it shall provide the remote set point to the flow controller RC4-FIC-811/ 812/ 813/ 814/ 815/ 816/ 817/ 818/ 819 respectively for 9 wells through PCS computer controller RC4-PY-811/812/ 813/ 814/ 815/ 816/ 817/ 818/ 819 TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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respectively for 9 wells which shall also take the measured value of downstream pressure RC4PI-821/ 822/ 823/ 824/ 825/ 826/ 827/ 828/ 829 on PCS through local pressure transmitters RC4-PT-821/ 822/ 823/ 824/ 825/ 826/ 827/ 828/ 829. For detailed modes of operation, refer Gaslift Operation philosophy of VSP platforms. Two chock valves are provided from main header to one bypass header to provide controlled gas in case of maintenance of the main flow control angle valves.

7.8.3

GASLIFT USE FOR SLUG REMOVAL & FOR GAS DISPOSAL. As the disposal of Gaslift is related to the underwater pipes before RISERS which are Gaslift main pipe from RP-3 platform to RC-4 Platform, Gaslift pipe to RC5 & RC-DM platforms, the take off point of this line are taken directly from three Gaslift Risers at RC4 platform. A shutdown valve RC4-SDV-802 is provided in the common disposal line. A chock valve is provided to throttle the flow. As this line is also to be used for removal of the slug accumulation in the Production separator gas outlet line whose design pressure is 60 barg so high pressure protection levels are given by providing three pressure transmitters RC4-PT803A / 803B / 803C. On actual high pressure in this section of gaslift line after chock valve during disposal or slug removal, the indication from these three pressure transmitters shall generate Pressure High High alarm signals in PLC and based on the “2 out of 3” voting system, PLC shall activate the Pressure High High interlock RC4-PAHH-803 which shall shutdown the RC4-SDV-802 in the gaslift disposal line.


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SHEET 45 OF 48

As 2nd level of safety, a pressure safety valve RC4-PSV-801 is also provided in this gaslift section. As the disposal is to be done from high pressure to low pressure through chock valve, there is potential of low temperature in this section if the disposal is not controlled properly. So a low temperature protection is given by providing a temperature transmitter RC4-TT-804 which shall generate the low temperature alarm signal in PLC and PLC shall activate RC4-TALL-804 to shutdown the RC4-SDV-802 in gaslift disposal line.

7.9

CHEMICAL INJECTION SYSTEM The Chemical Injection System includes dosing of the following Chemicals:

7.9.1

•

Depressant

•

Demulsifier

DEPRESSANT Depressant Unloading is done from container by Unloading Pumps (H-700A5-1/ H-700A5-2). There are four Depressant Storage Tanks E-700A2-1, E-700A2-2 with capacity of 10 M3 each and E-700A3-1 & E-700A4-1 with capacity of 20 M3 each. Chemical can be transferred from Jack-up drilling Rig to storage tank. TECHNICS OFFSHORE ENGINEERING PTE LTD, SINGAPORE PROCESS CONTROL PHILOSOPHY


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Depressant Dosing pumps H-700A1-01/700A1-02/ 700A1-03/ 700A1-04/ 700A1-05/ 700A106/ 700A1-07/ 700A1-08/ 700A1-09/ 700A1-10/ 700A1-11 are pneumatic operated pumps and the pumps discharge has provision to inject the chemical to two different points which are XMas tree at down hole & at upstream of flow choke valve at well head. To start the dozing pump, instrument air valves (RC4-XV-711/ 712/ 713/ 714/ 715/ 716/ 717/ 718/ 719/ 720/ 721) are to be opened which can be done by local hand switches RC4-HS711AA / 712AA/ 713AA/ 714AA / 715AA/ 716AA/ 717AA/ 718AA/ 719AA/ 720AA/ 721AA respectively and similarly to stop the pump, same instrument air valves are to be closed which can be done by either local hand switches RC4-HS-711AB / 712AB/ 713AB/ 714AB / 715AB/ 716AB/ 717AB/ 718AB/ 719AB/ 720AB/ 721AB respectively OR from remote hand switches RC4-HS-711B/ 712B/ 713B/ 714B/ 715B/ 716B/ 717B/ 718B/ 719B/ 720B/ 721B on PCS. There is trip of individual pump based on PSD-Well flow lines but the two common Deprassant Chemical injection pumps H-700A1-10/700A1-11 shall not trip on any individual Well PSD actuation. But if it is lined up towards any shutdown well then it is required to stop manually which is to be ensured through proper operating procedure and alarms.

7.9.2

DEMULSIFIER Demulsifier Unloading is done from container by Unloading Pumps (H-700B5-1/ H-700B5-2). There are two Demulsifier Storage Tanks E-700B2-1, E-700B2-2 with capacity of 2 M3 each. Chemical can be transferred from Jack-up drilling Rig to storage tank.


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Demulsifier Dosing pumps H-700B1-01/700B1-02/ 700B1-03/ 700B1-04/ 700B1-05/ 700B106/ 700B1-07/ 700B1-08/ 700B1-09/ 700B1-10/ 700B1-11 are pneumatic operated pumps and the pumps discharge has provision to inject the chemical to two different points which are XMas tree at down hole & at upstream of flow choke valve at well head. To start the dozing pump, instrument air valves (RC4-XV-761/ 762/ 763/ 764/ 765/ 766/ 767/ 768/ 769/ 770/ 771) are to be opened which can be done by local hand switches RC4-HS761AA / 762AA/ 763AA/ 764AA / 765AA/ 766AA/ 767AA/ 768AA/ 769AA/ 770AA/ 771AA respectively and similarly to stop the pump, same instrument air valves are to be closed which can be done by either local hand switches RC4-HS-761AB / 762AB/ 763AB/ 764AB / 765AB/ 766AB/ 767AB/ 768AB/ 769AB/ 770AB/ 771AB respectively OR from remote hand switches RC4-HS-761B/ 762B/ 763B/ 764B/ 765B/ 766B/ 767B/ 768B/ 769B/ 770B/ 771B on PCS. There is trip of individual pump based on PSD-Well flow lines but the two common Demulsifier Chemical injection pumps H-700B1-10/700B1-11 shall not trip on any individual Well PSD actuation. But if it is lined up towards any shutdown well then it is required to stop manually which is to be ensured through proper operating procedure and alarms.

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Process Control Philosophy

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