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.

为了提高采收率，已经进行了许多研究以循环注水（CWI）进行，而大多数目标油藏都是常规油藏，因此在超低渗透油藏中应用CWI的研究是有限的。在这项研究中，实验和数值模拟相结合被用来评估超低渗透油藏的CWI性能。结果表明，加压时间短而减压时间长，则水突破的可能性较低，且油水交换和再分配有足够的时间，具有较好的采油效率。另外，高压压力是对储层能量的良好补偿，并将水推到较远的区域以驱替更多的石油。对位于鄂尔多斯盆地的超低渗透油藏进行了数值模拟，进一步评估了岩心规模试验的最佳运行参数，并发现了实验与模拟结果的一致性。在模拟中，加压周期的最佳喷射周期和最佳喷射压力分别为20天和14 MPa。减压周期的最佳喷射周期和最佳喷射压力分别为60天和2 MPa。实施优化参数后，已实现了良好的现场响应。这项工作是首次系统研究CWI技术在岩心规模和储层规模下应用于超低渗透油藏的性能，