Permeability and Energy Evolution Characteristics of Heterogeneous Coal and Rock Mass

The coupling characteristics of stress, fracture, and seepage fields are significant to gas extraction and water-preserved mining. In this paper, a theoretical model and a numerical model of stress-fracture-seepage coupling in heterogeneous rock, including the division of elastic-plastic state and permeability characterization method, are proposed and verified. The effect of the homogeneity coefficient on rock mechanical properties, permeability, and acoustic emission (AE) evolution during fracturing was analyzed. The results show that the permeability of fractured samples exceeded that of elastic samples by two orders of magnitude, and both types of samples exhibit high-stress sensitivity in the low-pressure stage. The permeability and damage value grow gradually, showing an S-shaped pattern and a certain lag. Horizontal and vertical permeabilities were negatively correlated with heterogeneity. The sample failure mode changed from diffusion state to localization. A large homogeneity coefficient corresponded to an earlier localization, a lower fracture surface complexity, and a minor axial strain difference of the two critical energy thresholds. The fracture surface can be described by the spatial position of high-energy AE, and the AE thresholds corresponding to different homogeneity coefficients were the same. It is more reasonable to describe the characteristics of mine water and gas migration by taking a combined form of equivalent permeability and seepage path.