production control systems

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Jacek S Stecki is Chairman of the Subsea Engineering Research Group at Monash University and Associate Professor for the university’s Department of Mechanical Engineering. He is also Chairman of the Scientific Committee of Fluid Power Net International and Director of 94th Peso Pty Ltd. Professor Stecki has had 15 years’ industrial experience in Poland, Australia, the UK and Switzerland. He has been a visiting professor at the Denmark Technical University, National Research Council (Cemoter), Norwegian University of Science and Technology and University of Bath. He has also served as a consultant for BHP Petroleum, Brazil, and Asea Brown Boveri AG, Switzerland. Professor Stecki is a member of the Australian Computer Society, the Society of Automotive Engineers and the Institution of Mechanical Engineers and he has published over 100 technical papers and articles in international journals and conference proceedings, mostly on hydraulic control systems. a report by Professor Jacek S Stecki Chairman, Subsea Engineering Research Group, and Associate Professor, Department of Mechanical Engineering, Monash University Introduction Over the last decade, there has been a huge increase in the application of subsea systems for the production of oil and gas from subsea wellheads. A subsea production system comprises a wellhead, valve tree (‘x-mas tree’) equipment, pipelines, structures and a piping system, etc., and, in many instances, a number of wellheads have to be controlled from a single location. A subsea control system is part of a subsea production system, and proper performance of the control system is the critical factor in ensuring its reliable and safe operation. The control system provides operation of valves and chokes on subsea completions, templates, manifolds and pipelines. In addition to satisfactory operational characteristics, the design of a control system must also provide the means for a safe shutdown on failure of the equipment or on loss of hydraulic/electrical control from the topsite (a platform or floating facility) and other safety features that automatically prevent dangerous occurrences. One example of such a safety feature is the employment of fail-safe- operated subsea valves that close upon loss of hydraulic pressure. The control of various production functions, executed at the sea bed, is carried out from a topside production facility (a platform or a floating vessel), and a satisfactory response time for a control system is an important factor that may have a dramatic effect on reliability and safety of environmentally critical operations. As communication distance between topside production facilities and subsea installations increases, due both to multiple well developments and water depth, early methods of well control using direct hydraulic control of subsea valves have become less feasible due to operational limitations of such controls and due to both the size and cost of the multi-core umbilicals required to provide hydraulic power transmission. This has led to the development of more advanced and complex control methods using piloted hydraulic systems, sequential piloted systems and electrohydraulic systems (hard-wired and multiplexed). The complexity and performance characteristics of subsea control systems depend on the type of control used and are application-specific. The selection of the type of control system is dictated predominantly by technical factors like the distance between control points (offset distance between the platform and the tree), water depth, required speed of response during execution of subsea functions and type of subsea installation (single or multiple wellheads). To ensure reliable and safe operation of the subsea system, the design, operation and testing, etc., of a subsea control system is regulated by industry, national and international standards, and the systems are subjected to stringent quality review processes like failure modes, effects and criticality analysis, factory acceptance tests and reliability availability and maintainability analysis, etc. 1 Control Equipment – Topside Topside control system equipment comprises a hydraulic power unit (HPU), an electronic power unit (EPU) and a well control panel. The HPU provides high and low-pressure hydraulic supplies and is usually powered by electric motors, although redundancy is sometimes provided by air drives. The HPU includes tanks, pumps, a contamination control system and hydraulic control valves, etc. Emergency shutdown facilities are provided to bleed off hydraulic fluid and thus to close subsea fail-safe valves. The hydraulic components are fairly standard. Two types of fluid are commonly used for subsea production systems: high water content-based or synthetic hydrocarbon control fluids. The use of synthetic hydrocarbon control fluids has been infrequent in recent years, and their use is usually confined to electrohydraulic control systems. Water- based hydraulic fluids are used most extensively. The Production Control Systems – An Introduction BUSINESS BRIEFING: EXPLORATION & PRODUCTION 2003 1 Reference Section 1. P H Knight, et al. (1990), “Study of the performance and reliability of hydraulic, electrohydraulic and multi-functional umbilicals”, Engineering Research Centre, Offshore Energy Technology Board.

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Page 1: Production Control Systems

Jacek S Stecki is Chairman of theSubsea Engineering Research Groupat Monash University and Associate

Professor for the university’sDepartment of Mechanical

Engineering. He is also Chairman ofthe Scientific Committee of Fluid

Power Net International andDirector of 94th Peso Pty Ltd.

Professor Stecki has had 15 years’industrial experience in Poland,

Australia, the UK and Switzerland.He has been a visiting professor atthe Denmark Technical University,

National Research Council (Cemoter),Norwegian University of Science andTechnology and University of Bath.He has also served as a consultant

for BHP Petroleum, Brazil, andAsea Brown Boveri AG, Switzerland.Professor Stecki is a member of the

Australian Computer Society, theSociety of Automotive Engineers and

the Institution of MechanicalEngineers and he has publishedover 100 technical papers and

articles in international journals andconference proceedings, mostly on

hydraulic control systems.

a report by

P r o f e s s o r J a c e k S S t e c k i

Chairman, Subsea Engineering Research Group, and Associate Professor,

Department of Mechanical Engineering, Monash University

I n t r o d u c t i o n

Over the last decade, there has been a huge increasein the application of subsea systems for the productionof oil and gas from subsea wellheads. A subseaproduction system comprises a wellhead, valve tree(‘x-mas tree’) equipment, pipelines, structures and apiping system, etc., and, in many instances, a numberof wellheads have to be controlled from a singlelocation. A subsea control system is part of a subseaproduction system, and proper performance of thecontrol system is the critical factor in ensuring itsreliable and safe operation.

The control system provides operation of valves andchokes on subsea completions, templates, manifoldsand pipelines. In addition to satisfactory operationalcharacteristics, the design of a control system mustalso provide the means for a safe shutdown on failureof the equipment or on loss of hydraulic/electricalcontrol from the topsite (a platform or floatingfacility) and other safety features that automaticallyprevent dangerous occurrences. One example ofsuch a safety feature is the employment of fail-safe-operated subsea valves that close upon loss ofhydraulic pressure.

The control of various production functions,executed at the sea bed, is carried out from a topsideproduction facility (a platform or a floating vessel),and a satisfactory response time for a control systemis an important factor that may have a dramaticeffect on reliability and safety of environmentallycritical operations.

As communication distance between topsideproduction facilities and subsea installationsincreases, due both to multiple well developmentsand water depth, early methods of well control usingdirect hydraulic control of subsea valves havebecome less feasible due to operational limitations ofsuch controls and due to both the size and cost ofthe multi-core umbilicals required to providehydraulic power transmission. This has led to the

development of more advanced and complexcontrol methods using piloted hydraulic systems,sequential piloted systems and electrohydraulicsystems (hard-wired and multiplexed). Thecomplexity and performance characteristics of subseacontrol systems depend on the type of control usedand are application-specific. The selection of thetype of control system is dictated predominantly bytechnical factors like the distance between controlpoints (offset distance between the platform and thetree), water depth, required speed of response duringexecution of subsea functions and type of subseainstallation (single or multiple wellheads).

To ensure reliable and safe operation of the subseasystem, the design, operation and testing, etc., of asubsea control system is regulated by industry,national and international standards, and the systemsare subjected to stringent quality review processeslike failure modes, effects and criticality analysis,factory acceptance tests and reliability availability andmaintainability analysis, etc.1

Con t r o l E q u i pmen t – T o p s i d e

Topside control system equipment comprises ahydraulic power unit (HPU), an electronic powerunit (EPU) and a well control panel. The HPUprovides high and low-pressure hydraulic suppliesand is usually powered by electric motors, althoughredundancy is sometimes provided by air drives. TheHPU includes tanks, pumps, a contamination controlsystem and hydraulic control valves, etc. Emergencyshutdown facilities are provided to bleed offhydraulic fluid and thus to close subsea fail-safevalves. The hydraulic components are fairly standard.

Two types of fluid are commonly used for subseaproduction systems: high water content-based orsynthetic hydrocarbon control fluids. The use ofsynthetic hydrocarbon control fluids has beeninfrequent in recent years, and their use is usuallyconfined to electrohydraulic control systems. Water-based hydraulic fluids are used most extensively. The

Product ion Contro l Sys tems – An Int roduct ion

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Reference Section

1. P H Knight, et al. (1990), “Study of the performance and reliability of hydraulic, electrohydraulic and multi-functionalumbilicals”, Engineering Research Centre, Offshore Energy Technology Board.

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Product ion Contro l Sys tems – An Int roduct ion

characteristics of high water content-based controlfluids depend on the ethylene glycol content(typically 10% to 40%), and viscosity varies withtemperature (typically 2–10°C). As governmentregulations do not allow venting mineral-based oilinto the sea, if the system uses this type of fluid, itmust be a closed-loop system, which adds an extraconduit in the umbilical, making it more complex.Required fluid cleanliness for control systems is class6 of National Aerospace Standard (NAS) 1638.

A programmable logic controller or PC-based EPUmay be integrated with the platform control systemor it may be a self-contained unit.

Umb i l i c a l s

An umbilical is a conduit between the topside hostfacility and the subsea control system and is used forchemical and/or hydraulic fluids, electric power andelectric control signals. The hydraulic power andcontrol lines are individual hoses or tubesmanufactured from steel or thermoplastic materials(most common) and encased in the umbilical. Theelectrical control cables supplying power and controlsignals can either be bundled with hydraulic lines orlaid separately.

To avoid any potential faults, the umbilicals arefabricated in continuous lengths, i.e. without splices.Major problems encountered with umbilicals arepermeability to methanol, fluid incompatibility andmechanical damage during manufacture andinstallation. Current research and developmentefforts are directed towards improvement ofthermoplastic umbilicals. In some cases, it may beadvantageous to use metal umbilicals and it should benoted that, due to problems experienced withthermoplastic conduits in umbilicals, some operatorsare now using only stainless steel tubing fortransporting fluid in umbilicals. Umbilicalsemploying metal tubing are usually considered fordeepwater applications and when longer umbilicallengths are required. Metal umbilicals are alsoadvantageous when higher working pressures,greater electrical power requirements and continuousdynamic service are necessary. However, issues ofcorrosion, fatigue performance and end terminationsstill have to be resolved.

Con t r o l E q u i pmen t – S u b s e a

The production control system provides control ofall functions of the subsea production system. Theproduction control systems, as such, are onlyconcerned with controlling production and safetyvalves and monitoring devices and are not used toprovide control of subsea connector latching andunlatching or operation of vertical access valves, for

example. Typically, subsea functions includeoperation/control of:

• a downhole safety valve (DHSV);• subsea chokes;• production valves mounted on the x-mas tree; and• utility functions such as monitoring of fluid

characteristics, pressure leakage and valvepositions, etc. (see Figure 1).

Switching of the tree-mounted production valves oradjustment of chokes is by means of hydraulic, spring-return actuators. Typical fluid volumes associatedwith actuators of tree valves range from one to fourlitres, and, for DHSVs, only a few millilitres. Ahydraulic control system controls production valvesby supplying or venting valves’ actuators.

Typical operation pressures are 3,000psi (200bar) forx-mas tree functions, and 9,000psi to 12,000psi(600–800bar) for DHSV functions. Actuationpressures for tree valves and DHSVs vary widely asthey are a function of water depth and processpressures. The maximum expected actuationpressures occur during opening of valves that are inclosed, pressurised positions, typically as follows:

• tree valve open: 750psig to 2,200psig(50–140bar);

• tree valve closed: 600psig to 1,000psig(20–65bar);

• DHSV open – 2,500psig to 9,200psig(160–600bar); and

• DHSV closed – 500psig to 4,500psig (32–290bar).

T y p e s o f H y d r a u l i c C o n t r o l S y s t em

D i r e c t H y d r a u l i c

This is the simplest type of control system in whichHPU and well control panels for each individual wellto be controlled are located topside. Well controlpanels use solenoid-operated control valves.Hydraulic signals are transmitted via umbilicals toactuators of production control valves mounted onthe subsea tree. Each actuator of a tree-mountedproduction valve has a separate supply line. Theadvantages of this type of control system (see Figure2) are relative simplicity, high reliability, ease ofservice and minimisation of a number of subseacomponents. However, the umbilical is complexbecause it must contain all individual hydraulic linesfor all controlled tree components.

Direct hydraulic control systems are limited toapplications where the distance between theproduction facility and the subsea tree is less than3–4km. This limitation is due to low speed ofresponse of the system caused by the necessity to

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pressurise the fluid and transmit it between theproduction facility and the tree. The response of thecontrol system is influenced by both physicalproperties of hydraulic fluid, i.e. bulk modulus andviscosity, the characteristics of the umbilical, i.e. itsvolume, and compliance and volume of actuators. Atypical closing time for tree-mounted valves(actuator volume of three litres) when using a directhydraulic control and with an offset distance of 10kmis approximately eight minutes.

No feedback information on system subseaperformance is provided by the system; however,some information about subsea operations can beobtained by monitoring pressure in control lines andby measuring fluid supply and returns.

P i l o t e d H y d r a u l i c

In the piloted hydraulic control system, hydraulicpower to operate tree functions is supplied, via theumbilical, to a control pod and accumulator on thetree (see Figure 3). Umbilicals also contain individualhydraulic lines transmitting control signals to pilot-operated, spring-returned hydraulic valves mountedon the tree. Hydraulic valves direct fluid from theaccumulator to actuators of production valves andchokes. Use of pilot-operated valves improvesresponse of the system as only a control hydraulicsignal is transmitted from the topside to the tree. Inaddition, as the supply of fluid to actuators is fromthe accumulator rather than from a remote topsidelocation, the response time of tree valves is furtherimproved. However, the response time of the systemis still dependent on the volume of pilot lines andthus application of a piloted hydraulic control systemis limited to distances between the topside and thetree of up to 10km.

The umbilical termination for a piloted system can beidentical to that of a direct hydraulic system. Its designdepends on the method of umbilical installation andhook-up. The accumulators are usually mounted onthe tree and piped into the system. In some cases, theaccumulators are part of the control pod, whichallows retrievability. A separate, remotely retrievableaccumulator package is also used. The size of theaccumulator depends on the response timerequirements, umbilical hose type/size and thedistance between topside and tree location (offsetdistance). All subsea hydraulic-piloted control valvesare located in a control pod that is usually mountedon the tree frame. Depending on water depth anddiver access, etc., various types of pod are used,generally falling into two categories: remoteretrievable and diver retrievable. A remote retrievablepod is locked to a pod receiver plate, usually usingstab connections that interface control lines on thetree with the pod. Locking the pod to the receiver

plate is carried out either using a remote operationvessel or a hydraulically operated connector.

A piloted hydraulic system, like a direct hydraulicsystem, is highly reliable and easily accessible forservicing. Although the system performance is fasterand allows for larger offset distance, the pilotedsystem requires more complex hydraulic controlumbilicals and inclusion of tree-mountedcomponents, which adds to the cost of installation.As in a direct hydraulic system, a piloted system doesnot have direct feedback information aboutperformance of subsea functions, but, again, someinformation can be obtained by monitoring pressuresand flow at the topside.

S e q u e n t i a l P i l o t e d H y d r a u l i c

The basic set-up of a sequenced piloted hydraulicsystem is similar to a pilot-operated system; however,pilot-operated, two-position hydraulic valves areoperated in a predetermined sequence (see Figure 4).An independent operation of individual valves is notpossible in this system. Hydraulic control valves areconnected in parallel to hydraulic power supply linesfrom the topside. The sequencing is obtained bychanging the pilot pressure, which shifts the valvesinto an open position. The actuators of productionvalves are then moved in an order dictated by themagnitude of pressure. The system is relativelysimple and requires fewer hydraulic lines (see Figure4) with sequential piloted hydraulic system umbilicalsin comparison with a piloted hydraulic system. Anoperating sequence must be determined in advance,however, which provides less operating flexibilitythan either direct or piloted hydraulic systems. Theoverall response of the system is similar to theprevious system and, again, the only monitoring ofsystem operation is obtained at the topside bymeasuring fluid flow rate and pressure.

H a r d - w i r e d E l e c t r o h y d r a u l i c

The hard-wired electrohydraulic system is similar toa piloted system but uses solenoid-operated hydraulicvalves instead of hydraulically piloted valves (seeFigure 5). Like in a piloted system, hydraulic powerto operate tree functions is supplied by a subseaaccumulator connected, via an umbilical, to a topsidehydraulic power unit. A multiconductor electricalcable carries control signals from the topside tosubsea solenoid valves. The control pod containingthe solenoid operating valves and accumulator(s) islocated on the tree, and electrical connections areincluded in the control umbilical termination andbetween the pod receiver plate and the pod.

The advantages of hard-wired systems over theprevious three systems are:

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Reference Section

Page 4: Production Control Systems

Product ion Contro l Sys tems – An Int roduct ion

• a theoretically unlimited distance betweenproduction facility and subsea tree;

• independent control of selected functions;

• automatic sequencing if required;

• faster valve response than in previous systems;

• provision for data feedback from subsea functionsfor monitoring purposes; and

• a small control umbilical due to reduced numberof hydraulic lines in the umbilical, although this is,to some extent, offset by the necessity ofproviding a multiconductor electrical cable.

The electrohydraulic controls tend to be more costlyand less field serviceable than the other three controlsystems. Hard-wired systems are the most widelyused today; however, for new installations,multiplexed electrohydraulic is the preferred system.

M u l t i p l e x e d E l e c t r o h y d r a u l i c

This system is similar to the hard-wiredelectrohydraulic system but it takes advantage ofmultiplex technology to reduce the number ofelectrical lines and the complexity of subsea electricalconnections (see Figure 6). Electronic coding anddecoding logic is required at the surface and subsea,and a common cable supplies control signals(multiplexed digital data). This hydraulic power unitis mounted topside and supplies hydraulic power to atree-mounted accumulator. The control valves usedin these systems are normally latching types withpulse-energised solenoids, so the valves will stay inthe last commanded position when an electriccontrol signal is removed. To switch the valve, anelectrical control signal of a few seconds is required.

Two types of hydraulic control valves are used: directacting and pilot operated. The direct-acting,solenoid-actuated valves require a higher voltagecontrol signal than the pilot-operated valves. Whenpilot-operated valves are used, the control signalsactuate small pilot valves that direct the hydraulicfluid to either sides of the spools of the mainhydraulic valves, thus shifting the spools in thedesired direction and allowing hydraulic fluid toenter or leave actuators of the production valves.

The electronic module is built into the control podtogether with the hydraulic control valves, andinductive couplers are used to make and breakcircuits. Full monitoring can be integrated with

control functions without additional power andsignal transmission equipment. The system has goodsystem performance for long distances and is wellsuited for multi-well installations because the sameumbilical can serve many wells without reducingoverall performance. The simple umbilical allowsredundancy to be built in without compromising theumbilical capacity, but the drawback is increasedcomplexity subsea.

De v e l o pmen t T r e n d s

The significant cost associated with the design,manufacture and installation of subsea controlsystems provides incentives to improve the existingsystems and to invest in research for new systems.2

Basically, there are two schools of thought as to howto improve control of subsea completions, which arecharacterised by the development of:

• the Subsea Powered Autonomous RemoteControl System (SPARCS); and

• the Integrated Control Buoy.

These systems were developed with the aim ofreducing overall cost of control systems by removingthe need for umbilical and topside equipmentrequired for conventional systems.

S P A R C S

SPARCS3 has been developed by Kvaerner FSSL toprovide a low-cost control system solution formarginal oilfields (see Figure 7). It is a completelyself-contained power generation/control systemlocated at the wellhead. Communication with thetopside facility is via acoustic signal transmission, andelectric and hydraulic power required for valveoperations and monitoring functions is generated bya subsea turbine-driven generator. The systemcomprises two groups of components: a surfacecontroller and a subsea control unit.

The surface controller is located on the host platformand consists of an operator interface console, acoustictelemetry system and the required cables and powersupply. The acoustic telemetry system includes anacoustic transponder, transmitter/receiver andinterface to a directional hydrophone that can eitherbe clamped into position or, alternatively, deployedin a wireline system.

The subsea control unit is mounted near the well andprovides all the control and data-monitoringfunctions. Its major components are as follows:

B U S I N E S S B R I E F I N G : E X P L O R A T I O N & P R O D U C T I O N 2 0 0 3

42. P T Griffiths (1994), “HSE Development Trends”, Subsea and Data Acqusition, SUT.3. M C Theobald (1994),” FSSL Ltd, SPARCS Autonomous Control System”, Subsea and Data Acqusition, SUT.

Page 5: Production Control Systems

• a control module mounted near the wellhead andhousing valves and controllers;

• a hydraulic control module incorporatingsolenoid control valves;

• a hydraulic power unit including pumps, motors,accumulators and filters fitted with dual supplylines. The hydraulic power unit is a closed-loopsystem so all leakages and venting flows arereturned to the reservoir, which is fully pressure-compensated to ambient pressure. Hydraulic fluidis water-based.

• the electrical power supply generated by turbo-electric generator installed in the flowline spoolof the water injection. It converts the kineticenergy of the fluid into electrical energy and thusprovides continuous power to the control unit.An alternative power supply is provided by a thermoelectric generator clamped to aproduction flowline;

• a battery system is required to provide back-uppower for periods of peak power demands. It isinstalled and operated in an oil-filled environmentand uses flooded liquid electrolyte lead acid cells.A power conditioner system provides theinterface between the subsea generators and thebattery system. It also makes sure that the controlunit has priority over all other system powerrequirements; and

• the acoustic transponder system, which acts as a‘slave’ to the surface unit, i.e. it operates oncommand from the surface unit. It may,however, initiate transmission if a malfunctionof any subsea-located equipment in the subseaunit occurs.

The system design range is 10km. Plannedmaintenance intervals for the system vary betweentwo years (hydraulic fluid replacement and batteryreplacement) and five years (hydraulic filters,hydraulic motor, charge accumulators, transponderand electric generator).

The items with the highest research anddevelopment content, including the thermoelectricgenerator and the subsea hydraulic power unit, haveall been tested successfully.

I n t e g r a t e d C o n t r o l B u o y

The Integrated Control Buoy (ICB)4 has beendeveloped by John Brown Engineers andConstructors (see Figure 8). The buoy houses all

auxiliary systems required to operate and monitor thewell performance. Full control of the subseaproduction system is obtained from the host platformvia radio link to the buoy. The concept combinesproven systems (buoy control and monitoring,dynamic riser and radio communication) in a newconfiguration that utilises a moored buoy connectedvia a dynamic riser (umbilical) to the subseaproduction system. Buoy technology is field-provenand widely used in oceanographic andmeteorological data-gathering. The control systemon the buoy is fully autonomous, i.e. it will controlthe subsea production system without requiring acontinuous communication link to the host platform.Well parameters are measured and analysed by thebuoy control system and any required action is takenautonomously, i.e. without explicit command fromthe platform.

The system is designed to control and monitor all x-mas tree functions and critical subsea processparameters. All required safety back-up such asemergency shutdown and fire and gas systems arealso provided.

The dynamic riser (multi-bundle type comprisinghydraulic hoses, chemical injection hoses andinstrument/signal cables) provides the link betweenthe buoy and the subsea control system, distributeshydraulic and electric power and control to variousvalves and carries signals from monitoring devices.

Radio communication with the platform is via line-of-sight microwave link and takes place at regularintervals, controlled by the buoy. Typicalinformation transmitted is the well status(temperature, pressure, valve positions andhydrocarbon leakage, etc.) and on-board buoy status(fuel level and battery voltage level, etc.).

A cost study carried out comparing this systemwith conventional systems for a single satellite well15km from host showed substantial potential costsavings. The conceptual design of the system hasbeen completed and the system was installed insummer 1995.

Con c l u s i o n

This article provides a short, and by no meansexhaustive, review of subsea control systems in usetoday. The evolution of the system from a simpledirect hydraulic control system to more advancedelectrohydraulic systems has taken a long time. Thereason is the conservatism of the industry caused, tosome extent, by the necessity to meet stringentgovernment regulations. It is a major challenge to

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Reference Section

4. P Yates, et al. (1994), “Umbilical-less Integrated Control System”, Subsea and Data Acqusition, SUT.

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Product ion Contro l Sys tems – An Int roduct ion

introduce and receive acceptance of a new concept inthe offshore oil and gas industry. To even beconsidered, the system needs to be ‘proven’ in otherapplications or, alternatively, it needs to offer asignificant cost-saving potential. The SPARCS andthe Integrated Control Buoy systems presented in thisarticle bring new elements and technologies into well-established fields and offer potential large savings;however, it is likely to be some time before these

systems will be at a technological level where they canbe fully adapted by offshore oil and gas developers. ■

A c k n ow l e d g emen t

The author would like to acknowledge the contribution ofDr Jostein Alexanderssen of Pluggin SpecialistInternational AS, Norway, co-author of the paper onwhich this article is based.

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SeabedWellhead

Tree cap

SCSSV

ALM

ASV PSVPWV

CCV

ABVPLM

CIVPUM

PIGSTOP

Service

Production

Annulus bleed

ASM Annulus Swab ValveALM Annulus Lwer MasterPSV Production Swab ValvePUM Production Upper Master

PLM Production Lower Master

PWV Production Wing ValveCOV Cross Over ValveCV Check ValveCIV Chemical Injection Valve

ABV Annulus Bleed ValveSCSSV Surface Controlled Subsurface

Safety Valve

Figure 1: Subsea Production Valves

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SST

TC

UGB

Wellhead

Figure 2: Direct Hydraulic Control System

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SST

TC

UGB

Wellhead

Figure 3: Piloted Hydraulic System

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SST

TC

UGB

Wellhead

Figure 4: Sequential Piloted Hydraulic System

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SST

TC

UGB

Wellhead

Figure 5: Hardwired Electrohydraulic Control System

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SST

TC

UGB

Wellhead

Multiplexer

Figure 6: Multiplexed Electrohydraulic Control System

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Production flowlineThermoelectric generation

Water injectionTurbine generator

Hydraulic Actuators

Sensors

Acoustic transponder

+ -Electric Battery Data, Monitoring

& Control

Subsea power/control pod

Hydraulic Power Unit

Hydraulic Control

x-mas tree

SST

TC

UGB

Wellhead

Platform

Figure 7: SPARC System

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Platform

Flowline

Buoy

umbillical

x-mas tree

SST

TC

UGB

Wellhead

Figure 8: Integrated Control Buoy