Experimental and Numerical Simulation Study on the Two-Phase Threshold Pressure Gradient of Fractured Wells in Tight Gas Reservoirs

Abstract

Accurately predicting the production dynamics of multi-stage fractured horizontal wells in high-water-cut tight gas reservoirs remains challenging due to complex nonlinear flow regimes. This research aims to quantify dynamic threshold pressure gradients (TPGs) and their impact on well performance. A high-temperature, high-pressure flow testing system was utilized to measure dynamic TPG under varying water saturations in ultra-low-permeability cores. A dynamic mathematical model was established to characterize the exponential evolution of TPG. Furthermore, a comprehensive flow model was constructed using a coupled dual continuum–discrete fracture model. An entirely implicit numerical model utilizing a non-structured 3D tetrahedral mesh and a control volume finite element method enabled accurate numerical solutions. Key parameters such as water saturation, stress sensitivity, and fracture spatial asymmetry were systematically analyzed. Results: The threshold pressure gradient induces distinct dynamic boundary characteristics in pressure propagation, significantly reducing the wave propagation range compared to conventional models, with pressure drops concentrated near hydraulic fractures. Lower permeability (below 0.05 mD) and higher water saturation exponentially intensify the TPG amplification effect (exceeding 0.12 MPa/m), causing substantial reductions in both daily and cumulative gas production. The established simulation framework accurately captures the non-Darcy flow dynamics of fractured horizontal wells in high-water-cut tight gas reservoirs. It provides a reliable theoretical basis and computational tool for optimizing efficient gas field development.