Progress and reflections on the microcrack growth mechanism of hard-brittle shale under chemical-mechanical couplings

The temporal evolution of reservoir rock microcracks and other defects in the chemical-mechanical environment is the key issue causing rock strength deterioration and even macroscopic fracturing. It is of great significance to explore the development process of the cross-scale behavior of damage evolution induced by microcrack growth and destabilization damage induced by damage accumulation to ensure the stability of rocks surrounding the wellbore to efficiently explore and develop oil and gas resources. Firstly, three basic behaviors and characteristics of microcrack growth in rocks are introduced, and it is proposed that the hydration process of shale is the mechanism by which the internal microcracks continuously undergo more active subcritical growth, and the collapse instability of rocks surrounding the wellbore is more often manifested as the time-sequential damage evolution of microcracks from subcritical growth to dynamic fracture. Based on this understanding of the study of wellbore stability, in order to reveal the subcritical fracture mechanism of microcracks in rock under chemical-mechanical coupling, and to quantitatively characterize the damage evolution process and destabilizing mutation behaviors, the research team proposes the concept of "Chemical Fracture", which focuses on the fracture mechanics theory of microcrack growth in a chemical-mechanical environment, and the response of rock mechanical parameters to the structural damage evolution. Then the current research status of the subcritical fracture mechanism of rock chemical-mechanical coupled microcracks is summarized from the perspectives of theoretical modeling and experimental testing, respectively. Finally, several specific problems and challenges faced in the current research work are listed, and new thoughts and perspectives into microcrack growth evolution and fracture mechanisms of brittle rocks in chemical-mechanical environments are elaborated.