Breaking Oil Recovery Limit in Malaysian Thin Oil Rim Reservoirs: Force Balance Revisited

Abstract

Abstract The goal of an oil field development project is to accelerate the hydrocarbon production and optimize the recovery at the lowest cost. For a thin oil rim reservoir with a large gas cap on top and a strong aquifer below, achieving such goal can be very challenging since recovery of both oil and gas needs to be optimized. A successful project may entail plan first to accelerate the oil production with re-injection of the produced gas at the gas cap, maximizing the oil recovery prior to the start-up of the gas cap blow-down (Ref. 1–2). The maximum oil recovery factor achievable in thin oil rim reservoirs was evaluated for a Malaysian thin oil rim reservoir based on dynamic flow properties. The force balance between the gas cap expansion, aquifer expansion and viscous withdrawal (volumetric fluid production) was demonstrated by showing the model simulated water-oil and gas-oil contact movement. The understanding of the force balance progressively guided the field development project team to selectively re-activate some of the idle wells, to selectively place new additional infill horizontal wells, and to plan selective water and gas injection in key reservoir sectors. In this paper, the impact of changing force balance on oil recovery by increasing viscous withdrawal with increasing idle well re-activation and infill horizontal well drilling at their respective optimum produced gas re-injection was reported. This effort showed a potential of improving the current recovery factor from 35% up to 48%, at and above the estimated theoretical maximum oil recovery efficiency.