We use a 3D, fully coupled, fracture and fluid flow simulator to investigate the interactions between hydraulic fractures (HF) and pre-existing joints (J1 & J2), with stresses and joint characteristics based on typical Marcellus Shale properties. We consider two modeling scenarios in which we vary the orientation of the maximum horizontal stress (SHmax) with respect to the orientation of J1. Multiple stochastic realizations of the discrete fracture network (DFN) describing these joint sets, and two fluid viscosities end-members, were considered. Modeling results show that the fluid pressure perturbations extend to distances along J1 and J2 that are comparable to the microseismic (MS) event cloud, making joint shearing and "wet" events a probable consequence of the stimulation. Furthermore, the tendency of the main HF to be captured and offset by J1 and the extent of the offset depends in part on the fluid viscosity, the orientation of J1 with respect to SHmax, the length of J1, and the extent to which their height spans the zone of fracturable rock between the upper and lower fracture barriers. Comparing model predictions to MS interpretations suggests that the most probable geometric scenario for the pad site requires that SHmax and J1 are ~30 degrees apart.
The interactions between hydraulic fractures and geologic discontinuities, such as natural fractures, faults, and bedding that have been documented in sedimentary basins (e.g. the Appalachian Basin), where unconventional reservoirs are usually exploited, are very relevant to fracture stimulation design to enhance oil/gas recovery (Carlson and Mercer, 1991). An efficient fracture stimulation design, one that maximizes hydrocarbon recovery and reduces cost, should consider and possibly take advantage of these interactions, requiring a better understanding of the governing processes and the use of 3D fully-coupled reservoir simulators to effectively capture feedback mechanisms. Fracturing fluid can be diverted or "loss" into the discontinuities, which reduced the hydraulically fractured volume, but those preexisting discontinuities could also be stimulated, increasing the permeability pathways.