Bidirectional Coupling Simulation of Pressure-Saturation Decoupling to Enhance Fracturing-Flooding Performance in Low-Permeability Reservoirs

Abstract China's low-permeability reservoirs experience rapid production declines of 20-30% monthly, rendering conventional waterflooding methods ineffective due to inadequate injection pressures and limited sweep efficiency. To mitigate these issues, fracturing-flooding technology applies sustained high-pressure injections lasting 10-15 days above fracture gradients, facilitating enhanced fluid displacement through complex fracture networks. However, existing numerical simulation approaches struggle to accurately capture the dynamic evolution of reservoir properties during prolonged fracturing-flooding operations. This study introduces a bidirectional coupled modeling approach integrating geomechanical fracture analysis and reservoir fluid flow simulations. The framework simultaneously solves fluid flow and rock deformation equations, dynamically updating stress-dependent porosity and permeability, thereby providing improved predictive capabilities. Field validation shows the framework achieves less than 10% deviation in production history matching. The validated model reveals distinct propagation mechanisms: pressure fronts propagate rapidly, initially at 110 m/d and subsequently decreasing to 20 m/d, whereas saturation fronts advance at around 10.5 m/d, resulting in a clear velocity ratio of 2.2:1. Stress field analyses indicate notable reorientation of up to 40° near injection wells, contributing to complex fracture network formation. This modeling approach provides quantitative insights and practical guidance for optimizing fracturing-flooding operations, supporting improved management of pressure transmission and fluid displacement to enhance oil recovery in low-permeability reservoirs.