Optimum water alternating gas injection using compositional reservoir simulation

Abstract

Water alternating gas (WAG) injection is an enhanced oil recovery method that combines effect of water and gas flooding. This study is conducted to find the most suitable water-gas ratio and cycle size that yield optimal recovery. Black oil and compositinal reservoir simulations for a synthetic homogeneous reservoir are used for this purpose. The effects of horizontal permeability, vertical to horizontal permeability ratio, and distance between production and injection wells were also investigated. In this study, three phase Larsen and Skauge relative permeability hysteresis model was compared with the standard two-phase Killough hysteresis model. The results of the study show that WAG process, when appropiately implemented can yield higher recovery factor than waterflood. The impact of injected gas on increasing recovery efficiency was more evident in the compositional model than that in the black oil model. The results from the compositional model indicate that the smaller the cycle size, the higher the recovery factor will be and the water-gas ratio of 0.25 provides the highest recovery. Horizontal permeability, vertical to horizontal permeability ratio, and distance between producer and injector do not have an effect on optimal values of water-gas ratio and cycle size although they affect the absolute values of the recovery factor. The impact of using different relative permeability hysteresis was also found.