Micromechanical analysis of hydraulic fracturing in granite with a grain-based DEM coupled with pore network model

ABSTRACT: Rock is a typically heterogeneous material composed of inherent microstructures at the grain scale, which has a significant effect on the behavior of hydraulic fractures. This paper employs the grain-based DEM coupled with pore network model to capture the interaction behavior between hydraulic fractures and the inherent microstructures of rock. The numerical model is calibrated with experimental results of the Pocheon granite, and verified by the reference solution for a plane strain KGD hydraulic fracture. The simulation results indicate that mineral distributions and the strength difference between mineral grains and grain boundaries significantly impact on the hydraulic fracture growth. The fracture length and symmetry of hydraulic fractures for different spatial distribution of mineral grains differ widely. The tensile strength of grain boundaries increases with the PB tensile strength coefficient, resulting in the decrease of multi branches and intergranular fractures. Besides, the fractures near the fracture tip subjected to tiny fluid pressure resembles the fluid lag, which decreases with intergranular strength.