Optimization and Application of Unstable Water Injection in Fracture-Developed Zones of the KT-I Reservoir in Kazakhstan’s B Oilfield

The KT-I reservoir in the A well area of the B Oilfield exhibits strong reservoir heterogeneity and well-developed fractures. With the progression of water injection development, severe water channeling and flooding have occurred in the region, causing water-cut levels in oil wells to rise sharply after water breakthrough, eventually leading to production shutdown. Influenced by fractures, injected water channels through fracture-developed zones, forming directional water-flooding pathways. Outside these pathways, the degree of remaining oil recovery is low, resulting in residual oil retention zones. This study employs numerical simulation methods to investigate the applicability of unstable water injection methods. By leveraging pressure disturbances during unstable water injection cycles, the sweep efficiency of injected water is expanded, and the recovery of residual oil outside the water-flooding pathways is enhanced. The study compares the development effects under different water injection methods, cycle water injection volumes, and water injection cycle conditions. The results indicate that the asynchronous water injection method, with a cycle injection volume ratio of 1.7:0.3 for increased and decreased injection and a 30-day injection cycle, achieves the best experimental effect. Field application results in the A well area of the KT-I reservoir in the B Oilfield demonstrate that unstable water injection can improve the development performance of high-water-cut well groups in fracture-developed areas and has potential for application in similar well areas or reservoirs.