Investigating Hydraulic Fracturing Complexity in Naturally Fractured Rock Masses Using Fully Coupled Multiscale Numerical Modeling

Naturally fractured rock mass is highly inhomogeneous and contains geological discontinuities at various length scales. Hydraulic fracture stimulation in such a medium could result in complex fracture systems instead of simple planar fractures. In this study, we carried out fully coupled multiscale numerical analysis to investigate some key coupled processes of fluid-driven fracture propagation in naturally fractured rock mass. The numerical analysis follows the concept of the synthetic rock mass (SRM) method initially developed in the discrete element method (DEM). We introduce a total of five case study examples, including fracture initiation and near wellbore tortuosity, hydraulic fracture interaction with natural fractures, multi-stage hydraulic fracturing with discrete fracture network (DFN), in-fill well fracturing and frac hits after depletion-induced stress change, and induced seismicity associated with fault reactivation. Through those case studies, we demonstrate that with an advanced numerical modeling tool, the complex fracturing associated with hydraulic fracturing in naturally fractured rock mass can be qualitatively analyzed and the extent of various uncertainties can be assessed.