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Presentation on theme: " 1 Total System Optimisation in Gas-Lifted Fields ASME/API/ISO Fall 2003 Gas-Lift Workshop, Kuala Lumpur, October 21-22, 2003 ZR."— Presentation transcript:

1 1 Total System Optimisation in Gas-Lifted Fields ASME/API/ISO Fall 2003 Gas-Lift Workshop, Kuala Lumpur, October 21-22, 2003 ZR Lemanczyk & CJN McKie Edinburgh Petroleum Services

2 2 Optimisation in Gas-Lifted Fields Optimisation: maximisation of benefit subject to constraints imposed by external conditions and the performance of the producing system –Reservoir –Wells –Pressure drops in pipes –Performance of surface equipment –Delivery pressures

3 3 Lift Gas -$ Oil Water +$ -$ Export Gas +$ Lift Gas Single Well Optimisation Gas Injection Rate Oil Production or $/day Increasing THP P Q

4 4 Single Well Optimisation Assumptions –Fixed tubing head pressure for all gas lift rates –Lift gas is available to the well at the rate and pressure required Considered in the optimisation –Combined reservoir inflow and tubing outflow performance Not considered in the optimisation –Effect of other equipment on the well and vice-versa –How lift gas is supplied to the well –Whether lift gas injected into this well would give more benefit in another well

5 5 Prod Manifold Oil Water +$-$ Export Gas +$ Lift Gas -$ Lift Gas -$ Multi-well Optimisation Flowlines Flowline Flowlines

6 6 Multi-well Optimisation Assumptions –Fixed separator pressure –Fixed total lift gas availability Considered in the optimisation –Interactions between wells in production gathering network –Optimal allocation of limited supply of gas between wells Not considered in the optimisation –How lift gas is supplied to the well –How changing operating conditions affect total amount of lift gas available

7 7 Oil Water Export Gas Fuel Gas Lift Gas Lift Gas Manifold Prod Manifold +$-$ +$ -$ External Fuel Supply Total System Optimisation P P P P P P P P Q Q Q

8 8 Compressor Performance Speed Power 100% Decreasing Efficiency Gas Turbine Stonewall Surge Suction Flowrate Discharge Pressure Increasing Speed Compression Stage Fuel Gas

9 9 Valve Tubing Relationship between CHP and Qgi Ptub at operating valve Gas Injection Rate CHP Gas Injection Rate Increasing CHP

10 10 Well E Performance

11 11 WPS for GL Optimisation Well Completion Details Tubing Gas-lift Valves Open interval(s) Reservoir completion Reservoir Pressures kh, Skin, PI Production Tests FBHP, FBHT Observations Flowing Gradient Surveys Production System Geometry/Dimensions Well Active/Inactive Statuses Production Choke Sizes Current Flow Routing (Block Valve Statuses) Surface Eqpt Active/Inactive Statuses Current Pressures and Flowrates Economic Parameters Well Performance Surfaces Optimiser Recommendations

12 12 Solution Technique A model is constructed containing all of the wells, the gathering & distribution networks and the surface equipment The optimal solution to the model is found using Sequential Linear Programming (SLP) –Generic optimisation capability which can be applied to many different types of problems –Simultaneous simulation and optimisation –Proven ability to handle large, non hierarchical networks with loops and branches and hundreds of wells

13 13 Automation & Optimisation Off-line –Data input manually into system model –Results from system model implemented manually Open loop –Data input automatically into model from SCADA –Results from model implemented manually Closed loop –Data input automatically into model from SCADA –Results from model implemented automatically via set point controllers –Operator review may be required to ensure that implemented results are sensible

14 14 Open Loop Optimisation Optimiser Field OPERATOR Advice Approval Implementation Automatic Data Input Data Output OPERATOR Advice Approval Implementation Data Output Setpoint Controllers Closed Loop Optimisation

15 15 performance curves Offline Optimization Workflow Production Report Enter and validate production test data, re-tune well models Import updated well models into network models Update network model Corporate economic parameters Current production equipment and network status Run optimization Review and output optimiser results Implement in field Update corporate information systems Archive well and network models used for optimization Process takes weeks Highly skilled resource required

16 16 Why Online? Large Number of Wells Complex optimisation problem Reduce cycle time –Optimisation-to-implementation –Engineers time concentrated on value adding tasks Goals –Automate Process –Automate Repetitive Tasks –Optimise

17 17 Sustainable Production Optimisation Time Increased Value Over Do Nothing Simple Manual Optimisation Complex Manual Optimisation (Offline) Complex Automated Optimisation ( i -DO) Gains Sustained Gains Optimisation gains revert to norm as system changes: automation of process is key to sustain the gains

18 18 SCADA Server Server Web Client Online Optimisation SCADA Historian Expired Data Conditions, Status Optimized Set-points Results Targets LAN/WAN/Internet/Intranet Review, Approval Engineer PCs Well Perf Curves Network Model and Optimizer Historical Data Real-time Data Production Data Management Production Tests Well Models Corporate Database Economic Parameters Process takes minutes Fully automated Process Data

19 19 Conclusions Optimisation considering the total system can deliver additional production gains and costs savings over and above considering the production gathering network alone The capability to perform total system optimisation in gas-lifted fields exists today. A number of online gas lift optimisation systems have been installed and are operational today.

20 million BOPD Case Study: PDVSA - Venezuela Lake Maracaibo, Venezuela Large-scale implementation of gas lift Pilot Area (Centro Lago) –Over 200 wells –4 separation plants –5 compressor trains –10 lift gas manifolds 1.5 million BOPD MARACAIBO CABIMAS

21 21 Case 1: PdVSA On-Line –SCADA data automatically loaded to give current block valve and compressor status and to constrain the optimisation to stay close to existing operating conditions –Price/cost and equipment constraint data loaded from Corporate databases –Gas injection well set-points sent directly to SCADA controllers (after production operator review as a block) –Recommended pressure control valve set-points and compressor operating conditions sent to production operators in open-loop advisory messages –Results stored in central database for access by other applications.

22 22 Oil Water Export Gas Lift Gas Optimal Separator Pressure Separator pressure has to be high enough to transfer gas to compression plant Total System Optimisation showed that it was possible to simultaneously reduce Psep and Qgi 3% increase in oil production, 14% decrease in lift gas requirement Significant Pressure Drop From Wells To Wells

23 23 Field Implementation Results

24 24 KOC POIS In 2000 KOC awarded a contract for Production Optimization and Information Systems to a consortium including EPS Objective - Deliver an integrated optimization and advisory system interfacing to the automation and SCADA systems covering four fields in North Kuwait Scope –Four fields in North Kuwait including 411 well strings –Of these 33 are water injectors, 91 gas-lifted producers, and 30 wells producing with ESPs. –Complex network configuration allows wells to be switched between high, medium and low pressure separators as well as between wet and dry trains.

25 25 KOC POIS Production Operation Information System (POIS) EPS in partnership with Aspentech On-Line Optimisation (inc. GL) implemented NF + 91 GL + 34 ESP + 33 Injectors = ~400 wells 5 Fields; 8 Producing Layers; 13 Fluid Models 600,000 bopd 217 SCADA – RTU Systems Engineering support contract awarded 2003 despite intense competitive pressure

26 26 Abdali: 16 Wells to 2 GC via 13 6in lines Ratqa: 20 Wells to 2 GC via 36in & 10in lines Raudhatain: 195 Wells to 3 GC thru 7 MF each Sabriyah: 142 Wells to 1 GC thru 7 MF Bahra: 5 Wells to 1 GC thru 7 MF 378 producers connected to 3 GCs through of 21 headers KOC POIS

27 27 Lift-Gas System 5x7 Possible inputs from RQ & AD fields 9 Sub-sheets holding wells each 7x3 MF interconnecting all 194 wells across the field 7x3 MF outlets to production terminals Lift gas to SA field Inside Raudhatain KOC POIS

28 28 NP & GLwells (FG) Multi-header choice for lift-gas at present & for future Multi-MF choice for production at present and for future KOC POIS Inside Raudhatain Subsheet RA-1

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