Improvement in Oil Recovery Through Pro-Active Reservoir Management for a High Value Asset – A Case Study

Abstract

Abstract fieldThe field, located 120 km offshore in the Malaysian deep water, was discovered in December 2003 and put on production in November 2012. As per the Field Development Plan (FDP), Reservoir Management Plan (RMP) for G-K field is to inject water and gas from the beginning of oil production in Pink1/2 and UK1 reservoirs. The objective of the study was to optimize the voidage replacement by WI, so as to maximize the up-dip oil recovery. The study was conducted on a sector model. A compositional PVT model, having 17 pseudo components, was developed. To explain the compositional variation in reservoir, the PVT variation has been incorporated. The SCAL data, same as used in FDP, have been used for the study. Two producers were considered in the sector model so as to study the oil movement between the two wells. One Injector each was placed in GCG and aquifer. For UK1 reservoir, the plan is to re-inject 60% of the produced gas from UK1. For PINK1/2, it is planned to re-inject all the produced gas from PINK 1/2 plus any remaining gas left after internal usage. The total VRR target for both the reservoirs is 1.0, and the remaining part of the voidage replacement is made up by water injection. The FDP RMP was reviewed, because it was thought that in view of the small gas cap size (m ratio about 0.2 for PINK1/2 and 0.18 for UK1) and limited Gas Injection capacity, making up VRR equal to one by WI may not allow GC to expand rapidly. During the study, the whole process of Gas Injection and water Injection was divided in two parts, viz, Pre-Gas Breakthrough period and Post-Gas Breakthrough period so as to separately assess the impact of limited gas injection capacity after gas breakthrough. For PINK1/2 reservoirs, WI at 25% of the Instantaneous Voidage Rate (IVR) provides the best recovery before gas breakthrough. To avoid gas flaring after gas breakthrough, WI rate has to be increased to 40% of the IVR. For UK-1 reservoir, WI at 35% of the IVR provides the best recovery. Due to this study, there is an improvement of about 10% oil recovery over FDP study, which is equivalent to over 70 MMSTB of oil. In UK1 even after this improvement, a significant amount of up-dip oil still remains un-swept. This may require additional gas injection or drilling infill wells up-dip to the present location. During FDP the study was conducted on a Black Oil model, the present study was conducted on a compositional model.