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Total System Optimisation in Gas-Lifted Fields

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Presentation on theme: "Total System Optimisation in Gas-Lifted Fields"— Presentation transcript:

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 1

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 2

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

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 4

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

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 6

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

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

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

10 Well E Performance 10

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 Well Performance Surfaces 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 Optimiser Recommendations 11

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 12

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 Results from model implemented automatically via set point controllers Operator review may be required to ensure that implemented results are “sensible” 13

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

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

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

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

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

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. 19

20 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 3.5 million BOPD 1.5 million BOPD MARACAIBO CABIMAS 20

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. 21

22 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 From Wells Significant Pressure Drop Water Oil To Wells Export Gas Lift Gas 22

23 Field Implementation Results

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 ESP’s. Complex network configuration allows wells to be switched between high, medium and low pressure separators as well as between wet and dry trains. 24

25 KOC POIS Production Operation Information System (POIS)
EPS in partnership with Aspentech On-Line Optimisation (inc. GL) implemented 253 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 25

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

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

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

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