Study on the Mechanism of Enhanced Water Injection for Improving Oil Recovery in Low-Permeability Reservoirs

The development of low-permeability reservoirs faces significant challenges, particularly regarding low recovery rates. Conventional water injection is often limited by poor injectivity and low waterflood efficiency. As a key technology to enhance development effectiveness, enhanced water injection requires a systematic investigation into its intrinsic mechanism for improving recovery. This study focuses on a typical low-permeability reservoir. Through laboratory experiments on rock fracturing and spontaneous imbibition, the mechanism by which enhanced water injection increases recovery rates is elucidated. COMSOL Multiphysics is employed to simulate the enhanced water injection process and examine the multi-field coupling patterns during injection. The results indicate that (1) low-permeability rocks in the study area exhibit strong oil–water exchange capabilities driven by capillary forces, with average imbibition capacity ranging from 0.6 to 0.7 g/cm3 and oil displacement efficiency between 20% and 30%; (2) fracturing experiments demonstrate that the injection of low-viscosity fluids at low flow rates (15 mL/min) can induce complex fracture propagation, thereby expanding flow pathways; and (3) the evolution of fluid–solid coupling is jointly governed by injection pressure and damage effects. Specifically, coupling intensity and fracture propagation potential increase with pressure, with optimal injection pressure ranging from 20 to 25 MPa. Rock damage exacerbates the nonlinear response of this coupling. This study combines experimental validation with numerical simulation to provide theoretical support for field practice.