The K-39 reservoir, the major producing interval of the K field in the ARII Offshore NW Java Contract area, has been studied for a possible waterflood/enhanced oil recovery program. Sedimentological study indicates that the K-39 sandstone was deposited in a NE-SW trending shelf sand bar complex in Middle Miocene time. Based on core and log data, the K-39 reservoir is divided into 3 major units (A, B. and C) corresponding respectively to the central ridge facies, ridge margin fades and inter ridge facies. For reservoir simulation purposes, the units are further divided into 10 layers, Al to A3, B1 to B5, and Cl to C2. Layers A2, 81, B3, B5 and C2 are reservoirs while layers Al, A3, B2, B4 and C1 are nonreservoirs. The average gross reservoir thickness is 84 feet while the average net reservoir thickness is 51 feet. Study results indicate that, in the K main block, the K-39 reservoir reserve is 37.2 MMBO. In addition, a reserve of 4.3 MMBO is in the K-4 block. The reservoir rocks are fine to very fine grained, glauconitic and arkosic sandstones with an average porosity and permeability of 27% and 152 and respectively. A dual porosity system, micro-porosity and macroporosity, has been identified. The unit A has the best reservoir quality while the unit C has the poorest quality. Among the nonreservoir intervals, Al, A3 and Cl are very continuous while B2 and 64 occur only locally. These tight streaks may act as permeability barriers during production and waterflood/ enhanced oil recovery. Using detailed core to log correlations, cutoff values were determined for the reservoir parameters. Gross and net/gross ratio isopach maps for each layer as well as porosity and permeability maps for each reservoir layer were constructed. The results are being used for the reservoir simulation process.
Authors : Eriwan Hutapea, Nusatriyo & C.H. Charlie Wu