Effects of In Situ Stress and Multiborehole Cluster on Hydraulic Fracturing of Shale Gas Reservoir from Multiscale Perspective

Hydraulic fracturing through a multiborehole cluster is a crucial technology for the enhancement of shale gas reservoir production. However, the impact of borehole interference and in situ stress on hydraulic fracturing is still unclear. This study developed a multiscale hydraulic coupling model by improving the algorithm of the traditional pipe domain model within discrete element method and the initiation and propagation of hydraulic fractures under in situ stress and three multi-borehole clusters were numerically studied. Numerical results indicate that fracture development is initially governed by bedding planes, followed by the maximum principal stress. Tensile fractures account for over 80% of the observed fractures. As the lateral pressure coefficient decreases from 1, the proportion of tensile fractures decreases, while shear fractures become more prominent. The circumferential stress primarily influences fracture propagation, while radial stress plays a key role in governing fracture connectivity. During hydraulic fracturing of multiborehole clusters, the vicinity of the boreholes is prone to stability loss, and the stress shadow significantly affects the generation of fracture network. These results can deepen our understanding on the fracture network development and provide a guidance for the application of hydraulic fracturing technology.