Investigation of crack propagation patterns on the borehole wall during single-borehole hydraulic fracturing under different in-situ stress ratios

To study the initiation, propagation, and mechanical behaviour characteristics of fractures on the wall of a single hole during hydraulic fracturing for in-situ stress measurement, and to improve the accuracy of stress direction discrimination in hydraulic fracturing in-situ stress measurement. This paper adopts methods such as theoretical analysis, numerical simulation, and experimental research. On the basis of obtaining basic mechanical parameters through rock mechanics tests, and using the Weibull distribution to describe the inhomogeneity of rocks, a model based on COMSOL software is constructed. It studies the laws and influencing factors of fracture propagation on the borehole wall under different stress environments. The simulation results show that under different stress conditions, the initiation direction of fractures on the borehole wall is mainly parallel to the direction of the maximum principal stress and perpendicular to the direction of the minimum principal stress. At the same time, the propagation and closure of fractures are jointly controlled by the mechanical properties of rocks and the in-situ stress field. In addition, natural cracks have little impact on the propagation of fractures on the borehole wall, and the propagation of hydraulic fractures is not affected by natural cracks. This research achievement provides a reliable theoretical basis for accurately identifying the direction of underground stress, and has important value in guiding tunnel support design, preventing and controlling rockburst and other engineering practices.