Experimental and simulation investigations of cyclic water injection in low-permeability reservoir

Many studies have been carried out to investigate the cyclic water injection (CWI) in enhancing oil recovery, while most of the target reservoirs are conventional, and the study for CWI in application to ultralow permeability reservoir is limited. In this study, a combination of experiment and numerical simulation was used to evaluate the performances of CWI in ultralow permeability reservoir. The results indicate that short pressurizing period but long depressurizing period gives the low possibility of water breakthrough and sufficient time for oil/water exchanging and redistribution, which achieves better oil recovery efficiency. In addition, high pressurizing pressure is a good compensation to the reservoir energy, and pushes the water into the far region to displace more oil. The optimized operation parameters for the core-scale experiments are further evaluated with numerical simulation of a realistic ultralow permeability reservoir located in Ordos basin, China, and consistent results between experiment and simulation are found. In the simulation, the optimal injection period and injection pressure during the pressurizing cycle are 20 days and 14 MPa, respectively; the optimal injection period and injection pressure during the depressurizing cycle are 60 days and 2 MPa, respectively. Good field response has been achieved after the implementation of the optimized parameters. This work, for the first time, systematically studies the performances of CWI technique in application to ultralow permeability reservoirs both at core scale and reservoir scale, and it provides theoretical and practical implications for enhancing oil recovery in similar types of ultralow permeability oil reservoirs.