Dynamic Response of Fracture Networks and the Evolution of Waterflood Fronts During Fracture-Flooding

This study investigates the dynamic response of fracture networks and the evolution of waterflood fronts during fracture-flooding in low-permeability and tight reservoirs. By establishing a discrete fracture model that incorporates geomechanical heterogeneity and natural fractures, and utilizing the Barton-Bandis criterion to describe fracture stress-sensitive behavior, the fracture-flooding process was simulated and analyzed under two scenarios: considering versus ignoring the time-varying stress effect. The results demonstrate that when the time-varying stress effect is considered, fracture conductivity gradually recovers with increasing injection pressure, as the elevated fluid pressure within the fractures reduces the effective normal stress, promoting elastic dilation of the fracture aperture. This is evidenced by the average conductivity coefficient increasing from 0.4 (near-closure) to 0.99 (fully open) during the injection period. This recovery mechanism promotes a “wall-imbibition-dominated” flow pattern. In contrast, neglecting this effect leads to a “fracture-tip-breakthrough-dominated” mode, causing poor front uniformity. Quantitative analysis of the front morphology confirms this improvement: the perimeter-to-area ratio decreased from 2.507 to 1.647, and the coefficient of variation dropped from 0.490 to 0.324. This research provides an important theoretical basis for optimizing fracture-flooding operations and enhancing oil recovery.