Permeability Stress Sensitivity of Natural Fractures: Experimental and Modeling Analysis Considering Porosity and Filling Degree

ABSTRACT: This study examines stress-dependent permeability characteristics in tight shale reservoirs through systematic analysis of naturally fractured core specimens from the Chang 71 formation. Laboratory investigations employing pulse decay methodology quantify permeability evolution under varying effective stress conditions (0-60 MPa), comparing matrix behavior with two distinct fracture types: shale-filled and tensile fractures. Experimental data demonstrate significant variations in compressibility coefficients across different media, showing tensile fractures exhibit 1.8-2.3 times greater pressure sensitivity than shale-filled fractures, while matrix components display the lowest compressibility. Comparative analysis of mathematical models reveals the piecewise exponential function achieves superior fitting accuracy (R2>0.96) compared to conventional exponential models, particularly under elevated stress conditions (30-60 MPa) where permeability reduction exceeds 85%. The research further develops a novel quantification approach for pore stress sensitivity that establishes a positive correlation between shale-filling volume and pressure sensitivity coefficients. These findings advance fundamental understanding of fluid transport mechanisms in fractured unconventional reservoirs while providing practical methodologies for optimizing reservoir simulation accuracy through improved characterization of stress-permeability relationships.