Mechanism of Coal Shear Failure during the Gas Desorption Process: Experiments and Models

During CH4 extraction of a coal reservoir, the permeability increases due to the stress relaxation of coal matrix shrinkage and gas desorption, which is caused by the damage and destruction of coal. The stress concentration near the extraction hole and the reduction of lateral stress promote the occurrence of shear failure during CH4 extraction. Although extensive research has been conducted on the compressive and tensile strength of coal, the mechanism of shear failure induced by gas desorption in coal is still unclear. Therefore, the stress state and shear failure characteristics of coal during the CH4 desorption process were analyzed through mechanical experiments under triaxial conditions and mechanical models of CH4 extraction in coal reservoirs. The CH4 desorption can significantly reduce lateral stress in coal until shear failure occurs, which is the coupling result of adsorption and stress. Through verification, the dual-pore mechanics model can calculate the critical gas pressure for shear failure. The shrinkage of the coal matrix leads to lateral stress relaxation and becomes the driving force to promote shear failure of the coal body. This study reveals the coupled response shear failure mechanism of coal seam extraction, which provides a research direction for a deeper understanding of the impact of coal shear failure on reservoir permeability and dust generation.