Publications

The effective exploitation of the thin oil rim in the Gunung Kembang field is particularly challenging because of the huge size of the overlaying gas cap, and the thickness of the oil rim varying between 25 to 40 feet gross pay interval, not to mention the sizeable water aquifer underlying the reservoir. Horizontal wells have been utilized since 1992 to enhance oil recovery by reducing gas and water coning. Nevertheless, oil recovery still remains around 3%. As the pressure depletes, horizontal wells pose higher risk than before. This is best evidenced in the second stage of horizontal drilling which was undertaken in 2004, where water breakthrough and total loss occurred. The plan to add more horizontal wells to add recovery coincided with the Plan of Development (POD) commitment to deliver gas by gas cap blow down. This paper represents a team effort to formulate an optimization strategy for maximizing oil recovery and revenue while delivering gas as committed in the POD. The integrated reservoir characterization that comprises a carbonate depositional study and reservoir simulation was conducted to best manage not only the drilling location but also the number of wells and production strategy for future horizontal wells. The carbonate depositional study used existing logs and core data to reveal the best potential oil zone in the Baturaja formation in terms of porosity and permeability. Meanwhile, a reservoir simulation grid was aligned with the zonation from the carbonate deposition model, after that the performance history of the existing 10 wells was matched to develop an improved strategy. Sensitivity analysis conducted demonstrated that locating horizontal oil wells in the upper oil rim near the gas oil contact proved to be the best strategy for depletion of the oil rim. Of the five scenarios developed, one scenario was selected to accommodate both oil recovery optimization and gas cap blow down. This scenario includes eight additional horizontal oil wells while utilizing their produced gas to accommodate gas commitment, without drilling another gas well. Oil recovery is expected to rise to about 8% while gas is being delivered according to the POD.