Enhancing oil recovery through immiscible water-alternating-CO2 in tight oil formations—a case study of Yaoyingtai Field in China

Tight oil reservoir is widely distributed around the world. Unfortunately, tight oil reservoirs characterize severe heterogeneity in layers and interlayers, and suffer rapid decline of oil production at the later stage of conventional water flooding while premature gas channeling. Based on tight oil formations from Yaoyingtai Field in China, we investigate the mechanism of immiscible water alternating gas and conduct the numerical simulation; results show that oil production decline rate drops from 33.3 to 4.4%, and oil recovery is enhanced by 5–10% after utilizing immiscible water alternating gas. Notably, key factors for this positive contribution are understanding and controlling the change of three-phase relative permeability during the process of immiscible water alternating gas flooding and associated law of gas breakthrough. The relative permeability heavily depends on the capillary force, displacement pressure, and the number of alternations, and the direction of the gas breakthrough is mainly along the high permeability channel or micro fissures.