Publications

Field “A” is a waterflooded field consisting of three Areas with multi-layered formation of L, A, B & C reservoirs. Area 1 is the closest to the Gathering Station, then Area 2 following with Area 3. The pressures in surface facilities, injectors, and the Gathering Station causes injection to enter Area 1 first, continue to Area 2, then to Area 3 so that the distribution of injection water is uneven. Area 1, especially the layer C reservoir, has high injection based on Fluid In Fluid Out (FIFO) ratio which is confirmed by high reservoir pressure and indications of flow from new wells in Area 1. Injection in Area 1 has exceeded 26,000 BWIPD above the target. The pressure gradient in C reservoir Area 1 is high, 0.47psi/ft, while the Central Sumatra Basin pressure gradient is below 0.45 psi/ft and above that value will potentially cause problems with Sub-Surface Integrity (SSI). Area 3 currently lacks injection with low pressure gradient of 0.17 psi/ft. The limited capacity of Field “A” Gathering Station causes the inability to directly decrease the injection without shutting off the producers for balancing the Gathering Station level and this will result in Loss Potential Oil (LPO). A collaboration of cross functional teams has optimized the injection in Area 1 and Area 3 through diversion of water injection by gradually reducing the choke setting in Area 1, fully opening the chokes in all injectors in Area 3, monitoring the Well Head Injection Pressure (WHIP) to ensure that it does not exceed the Maximum Allowable Wellhead Injection Pressure (MAWHIP), monitoring Water Injection Pump Pressure (WIP), and monitoring injection pipeline pressure. The team has conducted estimates of water injection pump discharge rate vs. discharge pressure to ensure WIP is running within safe limits and so avoid shutdown of the water injection pumps and all water injectors. This effort continues with figuring out the bottleneck in the surface injection network using integrated production modelling. Recommendations from the effort has been followed up with field execution and yielded an encouraging result of water injection increase as well as additional oil production. The work started by setting up multifunctional team discussions, building an integrated production model including surface facilities and wells, fine-tuning the model with actual data and operational knowledge, generating alternative injection scenarios, and selecting the preferred one which was safely executed in the field. We have succeeded in reducing the SSI issue by diverting ~27,000 BWIPD injection from Area 1 to Area 3, and partially to Area 2, and improving the FIFO ratio and injection pressure in Area 1 and 3. The estimated annualized gain is 3.2 MMBO which includes avoiding potential LPO due to balancing the Gathering Station level is ~ 220 BOPD or equivalent with $ 28,000/day. Through this initiative, the team has successfully reduced reservoir overpressure which had previously triggered the SSI issue, increased production, and eliminated LPO.