Simultaneous propagation of multiple hydraulic fractures in crystalline rock: A numerical investigation based on coupled fluid-solid discrete element framework

The simultaneous multiple hydraulic fracturing treatment has been extensively employed in Enhanced geothermal systems (EGS) to increase the complexity and area of artificial fractures. However, the interaction between hydraulic fractures (stress shadowing effect) often occurs, leading to unpredictable fracture paths and unsatisfactory production outcomes. In order to investigate the mechanism behind the stress shadowing during simultaneous multiple hydraulic fracturing in crystalline rock, this study proposes a Hydro-Grain-Texture Model based on discrete element method that can consider the effects of mineral heterogeneity and pre-existing microcrack anisotropy. The results demonstrate that the simultaneous multiple hydraulic fracturing results in crystalline rock are influenced collectively by the confining stress, injection point spacing, mineral heterogeneity, and microcracks anisotropy. Due to the lower strength of grain boundaries, hydraulic fractures are more prone to deflect along these boundaries under the influence of the stress shadowing effect during their propagation. Conversely, when the orientation of pre-existing microcracks is approximately parallel to the direction of hydraulic fracture propagation, their capturing effect can facilitate the ability of hydraulic fractures to overcome the stress shadow effect. • HGTM couples fluid–solid with a microcrack model for simultaneous multi-fracturing. • Mineral heterogeneity and microcrack anisotropy control hydraulic fracture behavior. • Fracture patterns reflect stress contrast, cluster spacing, and preexisting cracks. • Reveal the mechanism and impacts of stress shadowing in simultaneous fracturing.