Nonlinear Flow and Permeability Characteristics in Fracture Induced by Shale Self-Supporting Particles

The methane in situ explosive fracturing technology represents a promising approach for shale gas extraction. This fracturing process generates a significant amount of shale debris particles within the fracture channels, providing a self-propping effect that enhances the fracture network conductivity and compressive resistance. This study investigates the nonlinear flow behavior and permeability evolution in fractures induced by shale self-propping particles. Flow tests were performed on fractured shale specimens with varying particle sizes (20/40, 16/20, and 8/16 mesh) under confining pressures (2.5–15 MPa) and flow rates (10–150 mL/min). A quantitative analysis was conducted to evaluate fracture permeability sensitivity to flow rates and confining pressures. Results reveal that the particles dominate nonlinear flow behavior at low confining pressures (2.5–5 MPa), while fracture aperture becomes critical at higher pressures. Larger particles increase hydraulic aperture and permeability but introduce more inflection points in response to stress, reflecting structural adjustments. Additionally, permeability sensitivity to flow rate experiences a rapid decline with increasing flow rates, ultimately converging toward zero. Larger self-supporting particle sizes intensify the fluctuation in the changes of permeability–stress sensitivity with confining pressure. Finally, a three-dimensional permeability nonlinear predictive model, incorporating confining pressure and flow rate, strongly correlated with experimental data (R2 > 0.95). Pearson correlation analysis provides valuable insights into the relationship between the self-supporting particle size, model parameters, and permeability variations. These findings provide valuable insights into the nonlinear behaviors and permeability evolution of the shale self-propped fracture system, offering theoretical guidance for optimizing methane explosive fracturing techniques to enhance the fracture conductivity in shale gas reservoirs.