Dulang oilfield is a multistacked sandstone reservoir offshore Peninsular Malaysia with 19 years of production history. Water injection was implemented to supplement the partial water drive. To date, the field recovery factor is approximately 20%, prompting initiatives to increase the recovery. Based on encouraging results from pilot test and simulation studies, immiscible WAG (IWAG) injection was chosen as the recovery strategy in the recently concluded conceptual field redevelopment study.
Prior to full-field implementation of IWAG injection, optimization studies were conducted to maximize incremental recovery from IWAG injection with optimal cost. The case study presented in this paper is that of the E10–14 sand unit, which is one of the major producing sands in Dulang field. In conceptual development study, the expected ultimate recovery (EUR) is 163 MMstb or 49% of STOIIP, contributed partly by 14 infill wells and IWAG injection, according to results from 3D compositional simulation studies. This is an incremental of 15% or 50 MMstb over the expected recovery from the existing depletion strategy which is expected to yield 35% recovery. The same 3D reservoir model was then used for further optimization by performing modification sensitivity runs on a restoration program of idle wells, infill well locations and numbers and injection rate parameters. Location of infill wells were selected on the basis of mobile oil saturation at the end of simulation run with well restoration and production enhancement. Additional increase in oil recovery was obtained by focusing on mobilizing remaining oil saturation. This was achieved mainly by tuning the injection rate of WAG injectors located at the flank of the reservoir. Through multiple iterations, 52% (173 MMstb) recovery can be achieved from IWAG injection with only 6 infill wells, a marked reduction from the proposed 17 wells in the conceptual development plan. This represents an incremental recovery of 18%.
The performance of edge water injection in Dulang has not been consistent due to operational issues and this has affected the reservoir pressure & oil recovery. However going forward, improved water injection & later optimal WAG injection strategy utilizing existing wells as well as putting in additional drainage and injection points can help increase oil recovery.