Reactivation of heterogeneous shear veins during reservoir stimulation: Fracture interaction, stress perturbation, and induced seismicity

Fault zones can be highly lithified, often manifesting as veins or cemented faults. Understanding vein structures and their dynamic response to reservoir stimulation is essential for managing anthropogenic earthquakes; however, this remains poorly constrained. We implement a novel algorithm for full moment tensor inversion and decomposition within the Discrete Element Method (DEM) framework and enhance the pipe network flow model by dynamically updating the domain volume and fluid saturation at each time step. We inject fluids into a simplified fault zone model containing heterogeneous veins to capture their dynamic response to reservoir stimulation. We find that shear stress on the veins decreases upon fracture initiation around the borehole. Normal stress decreases until the hydraulic fractures reach the veins, after which it begins to increase. We also observe relatively high double-couple (DC) components during interactions between hydraulic fractures and shear veins, whereas non-DC components are more prominent during fracture propagation within the rock matrix. Effective friction decreases as fractures interact with the veins. We argue that pore pressure diffusion and poroelastic stress transfer play critical and synergistic roles in reservoir stimulation.