e-petroleumservices com Total System Optimisation in Gas-Lifted Fields

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

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

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

Single Well Optimisation • Assumptions e-petroleumservices. com – 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

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

Multi-well Optimisation e-petroleumservices. com • 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

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

Compressor Performance e-petroleumservices. com Gas Turbine Speed 100% Fuel Gas 8 e rg Decreasing Efficiency Increasing Speed Su Discharge Pressure Compression Stage Power 100% ll wa Stone Suction Flowrate

Relationship between CHP and Qgi CHP e-petroleumservices. com Ptub at operating valve Increasing CHP 9 Gas Injection Rate Tubing Valve Gas Injection Rate

Well E Performance e-petroleumservices. com 10

WPS for GL Optimisation e-petroleumservices. com 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

Solution Technique e-petroleumservices. com • 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

Automation & Optimisation • Off-line e-petroleumservices. com – 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” 13

Open Loop Optimisation Closed. Loop Optimisation e-petroleumservices. com Automatic Data Input Data Output Optimiser Data Output Field OPERATOR Setpoint • Advice Controllers • Approval • Implementation 14 OPERATOR • Advice • Approval • Implementation

Offline Optimization Workflow Production Report Current production equipment and network status • Process takes weeks Corporate economic parameters e-petroleumservices. com • 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 Implement in field 15 Archive well and network models used for optimization Update corporate information systems Run optimization Review and output optimiser results

Why Online? e-petroleumservices. com • 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

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

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

Conclusions e-petroleumservices. com • 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

Case Study: PDVSA - Venezuela e-petroleumservices. com • Lake Maracaibo, Venezuela • Large-scale implementation of gas lift • Pilot Area (Centro Lago) – Over 200 wells – 4 separation plants – 5 compressor trains MARACAIBO CABIMAS – 10 lift gas manifolds 3. 5 million BOPD 1. 5 million BOPD 20

Case 1: Pd. VSA On-Line e-petroleumservices. com – 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

Optimal Separator Pressure e-petroleumservices. com From Wells Water Oil To Wells Export Gas Lift Gas 22 Significant Pressure Drop • 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

Field Implementation Results e-petroleumservices. com 23

KOC POIS e-petroleumservices. com 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

KOC POIS • • 25 e-petroleumservices. com Production Operation Information System (POIS) EPS in partnership with Aspentech On-Line Optimisation (inc. GL) implemented 2000 -2002. 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

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

KOC POIS e-petroleumservices. com Inside Raudhatain 5 x 7 Possible inputs from RQ & AD fields Lift-Gas System Lift gas to SA field 9 Sub-sheets holding 20 -25 wells each 7 x 3 MF interconnecting all 194 wells across the field 7 x 3 MF outlets to production terminals 27

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 e-petroleumservices. com