The Samarang Field is a complex stacked reservoir system, consisting of multiple sand packages separated by thin but continuous shale layers. The general reservoir structure is a faulted anticline. Most reservoirs have an oil rim with associated gas cap and have some natural water influx.
During the redevelopment study for Samarang field, an extensive IOR/EOR study was performed, focusing on the largest reservoirs of the field. A full-field simulation model for the M reservoirs (over 25% of the field STOOIP) was built and calibrated with the historical production, pressure, and fluid-contact movement data. Using this model and various cross section models, an extensive investigation was conducted to evaluate the benefit of injecting water and hydrocarbon gas to improve oil recovery in these reservoirs. The results indicated that updip water injection into the gas-cap region of the reservoirs is beneficial in improving oil recovery. Simultaneous updip water and downdip gas injection gave the highest oil recovery, compared to other injection schemes. This Gravity Assisted Simultaneous Water and Gas injection scheme (GASWAG) improved the sweep efficiency of the lower section on the inner part of oil rim with the downward movement of water and at the same time, increases the swept efficiency of the upper section on the outer part of oil rim with upward movement of injected gas.
The investigated EOR schemes for M reservoirs could potentially increase the cumulative oil production by 20 MMSTB compared to infill drilling only. This increase represents ∼7% of OIIP. A significant fraction of this oil production can be produced by reactivating existing idle wells during the application of the EOR process. This paper describes the investigation of the gas and water injection to improve oil recovery in the M reservoir layers.