Study On Microstructural Evolution Of Rock Fractures Under Multi-Field Interactions

The complex rock fracture structures in reservoirs play an important role during methane extraction. However, there is still a challenge to elucidate the impacts of adsorption–desorption, rock expansion, and thermal conduction on the microstructures under thermal–hydrological–mechanical interactions. In this paper, fractal theory for porous media was applied to characterize the structures of rock fractures, and the fracture fractal dimension (Df) was adopted to analyze the density of fractures and the microstructural evolution. We developed a coupled thermal–hydrological–mechanical model enabling simultaneous analysis of rock fracture microstructures and multi-physical field effects. Furthermore, we analyzed the evolution of the fracture fractal dimension with the reservoir parameter effects, including: (1) methane extraction process; (2) reservoir stress; (3) pore pressure; and (4) reservoir temperature. We also calculated the effects of physical and mechanical factors on the above parameters, including (1) adsorption constant; (2) the in-situ stress; and (3) thermal expansion coefficient. The present results indicate that various characteristic parameters have multiple effects on the microstructures of rock fractures. It was found that the fractal dimension is inversely proportional to the reservoir stress, the gas pressure, and the reservoir temperature.