Experimental investigation of methane explosion fracturing in bedding shales: Load characteristics and three-dimensional fracture propagation

Methane in-situ explosion fracturing (MISEF) enhances permeability in shale reservoirs by detonating desorbed methane to generate detonation waves in perforations. Fracture propagation in bedding shale under varying explosion loads remains unclear. In this study, prefabricated perforated shale samples with parallel and vertical bedding are fractured under five distinct explosion loads using a MISEF experimental setup. High-frequency explosion pressure-time curves were monitored within an equivalent perforation, and computed tomography scanning along with three-dimensional reconstruction techniques were used to investigate fracture propagation patterns. Additionally, the formation mechanism and influencing factors of explosion crack-generated fines (CGF) were clarified by analyzing the morphology and statistics of explosion debris particles. The results indicate that methane explosion generated oscillating-pulse loads within perforations. Explosion characteristic parameters increase with increasing initial pressure. Explosion load and bedding orientation significantly influence fracture propagation patterns. As initial pressure increases, the fracture mode transitions from bi-wing to 4–5 radial fractures. In parallel bedding shale, radial fractures noticeably deflect along the bedding surface. Vertical bedding facilitates the development of transverse fractures oriented parallel to the cross-section. Bifurcation-merging of explosion-induced fractures generated CGF. CGF mass and fractal dimension increase, while average particle size decreases with increasing explosion load. This study provides valuable insights into MISEF technology.