Microstructural evolution and hydraulic response of shale self-propped fracture using X-ray computed tomography and digital volume correlation

Methane in-situ explosive fracturing technology produces shale debris particles within fracture channels,enabling a self-propping effect that enhances the fracture network conductivity and long-term stability.This study employs X-ray computed tomography(CT) and digital volume correlation(DVC) to investigate the microstructural evolution and hydromechanical responses of shale self-propped fracture under varying confining pressures, highlighting the critical role of shale particles in maintaining fracture conductivity. Results indicate that the fracture aperture in the self-propped sample is significantly larger than in the unpropped sample throughout the loading process, with shale particles tending to crush rather than embedded into the matrix, thus maintaining flow pathways. As confining pressure increases, contact areas between fracture surfaces and particles expand, enhancing the system's stability and compressive resistance. Geometric analyses show flow paths becoming increasingly concentrated and branched under high stress. This resulted in a significant reduction in connectivity, restricting fracture permeability and amplifying the nonlinear gas flow behavior. This study introduces a permeability-strain recovery zone and a novel sensitivity parameter m, delineating stress sensitivity boundaries for permeability and normal strain, with m-value increasing with stress, revealing four characteristic regions. These findings offer theoretical support for optimizing fracturing techniques to enhance resource extraction efficiency.