Modeling hydraulic fracturing in jointed shale formation with the use of fully coupled discrete element method

During a hydraulic fracturing treatment, sedimentary beddings and preexisting joints in the shale reservoir may cause the deviation of fractures and the diversion of fluid, which ultimately lead to the unexpected fracture patterns. To evaluate the influence of these factors on the fracturing response, a comprehensive study is conducted using the discrete element method simulations. Interactions between the beddings, the preexisting joints and the induced fractures are modeled in a fully coupled manner by idealizing the sedimentary beddings which cause inherent anisotropy as individual horizontal smooth joint and modeling any preexisting joints with continuous smooth joint contacts. The models are first calibrated to reproduce the mechanical properties of the anisotropic rock in field. Results from these simulations indicate that the formation's anisotropy promotes fracture growth along the sedimentary beddings. Joint characteristics (i.e., orientation, aperture, and healing conditions) could have a major impact on the behavior of shale formation during hydraulic fracturing operations. Open horizontal joints play a more important role in the fracture propagation process than the in situ stress under the stress state considered in this study. The healing in the joints creates a barrier for fracture propagation, which might be effective enough to lead to fracture deviation from the preferred orientation. This study reveals the important factors which may influence the hydraulic fracture propagation and thus can serve as numerical basis for the more exhaustive studies in the future, e.g., models with realistic fracture network and more complex injection scenarios.