Evaluation of combined water and gas dumpflood into oil reservoir

Abstract

Secondary recoveries such as water and gas flooding are commonly used in order to improve oil production. However, water and gas injection typically incurs high capital and operating costs. In multi-stacked reservoirs in which water aquifer is located above an oil reservoir with a gas reservoir underneath, water from the overlying aquifer and gas from the underlying gas reservoir can be dumped into the oil reservoir instead of injecting them from surface. In order to investigate the performance of combined water and gas dumpflood in comparison to stand-alone water dumpflood and stand-alone gas dumpflood, a hypothetical reservoir model with simple geometry having a moderate dip angle is constructed using a numerical reservoir simulator. Water dumping well is located in the downdip part of the reservoir system while the gas dumping well is located updip. The oil producer is located between the two wells. The sizes of gas reservoir and aquifer are varied in order to determine their effect on oil recovery. Simulation results show combination dumpflood is more favorable than other methods when there is a presence of large aquifer size and small gas reservoir. In cases of large gas reservoir, stand-alone gas dumpflood is better a method. In all the cases, stand-alone water dumpflood is worse than stand-alone gas dumpflood and combination dumpflood. To optimize oil production in case of combination dumpflood, the oil producer should be located a little bit towards the water dumping well in order to avoid early gas breakthrough. The results from simulation also indicate that simultaneous dumpflood of water and gas at the beginning of the production is the best choice for combination dumpflooding schedule due to its ability to maintain higher oil reservoir pressure at higher oil production rate.