Pore-scale modeling of hydromechanical coupled mechanics in hydrofracturing process

Hydrofracturing is an important technique in petroleum industry to stimulate well production. Yet the mechanism of induced fracture growth is still not fully understood, which results in some unsatisfactory wells even with hydrofracturing treatments. In this work we establish a more accurate numerical framework for hydromechanical coupling, where the solid deformation and fracturing are modeled by discrete element method and the fluid flow is simulated directly by lattice Boltzmann method at pore scale. After validations, hydrofracturing is simulated with consideration on the strength heterogeneity effects on fracture geometry and microfailure mechanism. A modified topological index is proposed to quantify the complexity of fracture geometry. The results show that strength heterogeneity has a significant influence on hydrofracturing. In heterogeneous samples, the fracturing behavior is crack nucleation around the tip of fracture and connection of it to the main fracture, which is usually accompanied by shear failure. However, in homogeneous ones the fracture growth is achieved by the continuous expansion of the crack, where the tensile failure often dominates. It is the fracturing behavior that makes the fracture geometry in heterogeneous samples much more complex than that in homogeneous ones. In addition, higher pore pressure leads to more shear failure events for both heterogeneous and homogeneous samples. Plain Language Summary Hydrofracturing is an important technique in petroleum industry to stimulate well production. Yet the mechanism of induced fracture growth is still not fully understood, which results in some unsatisfactory wells even with hydrofracturing treatments. This problem may not be solved in continuum scale so that we establish a pore-scale numerical framework to reproduce and simulate this process. The results show that the failure patterns in hydrofracturing are quite different from those in normal fracturing by pressure. The shear failure plays a very important role besides the tensile failure. The strength heterogeneity has a significant influence on hydrofracturing. A quantitative characterization of heterogeneity and fracture is proposed in this work. Predictions by this method agree well with existing experimental data for several cases. The results will improve understanding of mechanism of hydrofracturing mechanics and therefore help to optimize the hydrofracturing process in applications.