3D Modeling of Hydraulic and Natural Fracture Interaction

An advanced numerical model is developed to investigate the different aspects of stimulation in naturally-fractured rocks. A fully-coupled 3D HF–NF “GeoFrac-3D” model is developed and used to study hydraulic and natural fracture(s) interactions in 3D without any major assumptions concerning the intersection and coalescence. Rock deformation and stresses are modeled using three-dimensional displacement discontinuity (DD) method. Contact elements are used to represent the closed natural fractures along with the Mohr–Coulomb criterion to determine the contact status of the fractures. Fracture propagation is modeled using a mixed-mode propagation scheme. A novel fracture coalescence scheme is integrated in the 3D HF–NF model to investigate intersection problems for a wide range of NF dip angles and strikes. The simulation results indicate that hydraulic fractures experience pressure drop upon intersection with permeable natural fractures. The pressure drop is followed by an increase in the injection pressure as the hydraulic fracture pressurizes the natural fracture. Moreover, the results show that the HF may propagate in other directions away from the NF when it is partially arrested by the natural fractures. Simultaneous interaction with multiple NFs and/or stress barriers was found to result in complex HF geometries with non-uniform fracture aperture distributions that could, in turn, affect proppant placement.