Microscopic damage and permeability evolution of prefabricated fractured shale under hydro-mechanical coupling after heat treatment

To investigate the microscopic damage mechanisms of fractured shale under hydro-mechanical (HM) coupling after heat treatment, this study employs computed tomography (CT) scanning and three-dimensional (3D) reconstruction techniques to characterize the pore network. The 3D pore structure models and corresponding pore network models of fractured shale elucidate the mechanisms by which pre-existing fractures influence crack propagation pathways and facilitate the formation of complex fracture networks. The 3D fractal dimension demonstrates an inverse relationship with increasing confining pressure and temperature, which is accurately characterized by a bivariate polynomial function. The pore-throat size distribution demonstrates bimodal characteristics at 25 °C, with dual frequency maxima observed at smaller diameters (approximately 100 μm) and intermediate diameters (400−600 μm). As the temperature increases, the throat distribution shifts to a unimodal pattern, with the main peak shifting toward smaller diameters. Under confining pressure, the pore network undergoes progressive compaction, resulting in a notable reduction in macropore-throat prevalence and simultaneous homogenization of throat size distribution. Fractured shale specimens display bimodal pore diameter distributions, with pre-existing fractures significantly enhancing the evolution of pore space. Within the temperature range of 25−250 °C, both fracture development and permeability gradually decrease. However, intensified organic matter decomposition results in significant increases in porosity, connected porosity, and permeability at 350 °C. Elevated confining pressures exert suppressive effects on these petrophysical parameters, with interdependencies quantitatively described by a bivariate polynomial regression model. Permeability evolution demonstrates a strong power-law dependency on porosity variation. These findings will provide insights into structural evolution and flow in fractured shale, optimizing unconventional reservoir stimulation and integrity. • Revealed the role of prefabricated fractures in crack network formation. • Detailed the effects of temperature and confining pressure on pore and throat distributions. • Demonstrated the relationship between pore structure and permeability under HM coupling. • Proposed a model to characterize the evolution of porosity and permeability under HM coupling.