The goal of an oil field development project is to accelerate the hydrocarbon production and maximize the recovery at a 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 shall be maximized. A successful project shall entail plan first to accelerate the oil production maximizing the oil recovery prior to the gas cap blow-down.

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 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- cap gas injection in key reservoir sectors.

In this paper, the reservoir simulation study on simultaneous up-dip water and down-dip gas injection was reported. The down-dip gas injection, injecting gas at and close to water/oil contact, was found to be able to impede bottom aquifer advancement, improve sweep and further enhance the thin oil-rim oil recovery. The gravity assisted injection technique could become a cost effective alternate for IWAG particularly for remaining oil rim which can be less than 10 m after the successful primary and secondary production.

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