The interaction of hydraulic and natural fractures limits the successful hydraulic stimulation treatments and enhanced production in unconventional reservoirs. In this context, the numerical models become indispensable for understanding hydromechanical mechanisms present in the hydraulic stimulation and the production of naturally fractured formations. This work presents a fully coupled hydromechanical approach to study the hydraulic fracture stimulation in naturally fractured formations and its effect on the production performance in unconventional reservoirs. The proposed methodology is based on the finite element method (FEM) and includes the coupling of fluid flow and geomechanics within the permeable rock formation and the fracture propagation process. An intrinsic mesh fragmentation technique is used to simulate non-planar fracture propagation with complex crack patterns. A pore cohesive zone model is used to simulate hydraulic fracture propagation, and the Mohr-Coulomb failure criterion is adopted to model closure/opening and friction/shear dilation of natural fractures. Several scenarios considering a complex fracture network are investigated to understand the dominant factors influencing hydraulic fracturing and the production performance in unconventional reservoirs.


The hydraulic fracturing technique is dispensable in the development of unconventional reservoirs with ultralow permeability. The efficiency of hydraulic stimulation is strongly affected by the presence of geological discontinuities such as faults, joints, and natural fractures (Barbier, 2002; O’Sullivan et al., 2001). Geological discontinuities reduce the mechanical strength of the overall rock mass and alter the fluid flow characteristics. Pre-existing fractures can be partially or completely cemented. They can act as barriers for flow paths depending on the permeability of the filling material (Warpinski & Teufel, 1987). Sealed fractures can be stimulated by hydraulic fractures (HFs) and become preferential flow channels for oil/gas exploitation (Rueda Cordero, Mejia Sanchez, & Roehl, 2019a). In that sense, the hydraulic stimulation aims for the activation of natural fractures (NFs) and/or generation of new induced fractures to enhance permeability and well-reservoir connectivity (Shahid et al., 2016). However, the interaction of induced and pre-existing fractures increases the complexity of the hydraulic treatment and the geometry of the stimulated fracture network (Stephenson et al., 2018; Weng, 2015; Zhang et al., 2019).

Field and experimental observations showed different interaction types between induced and natural fractures (Jeffrey et al., 2010). Figure 1 illustrates the interaction process between fluid-driven fractures and pre-existing discontinuities. During the injection process, natural fractures can act as preferential paths for the growth of the hydraulic fracture network or arrest the hydraulic fracture propagation in some directions (Wang, 2016). In some cases, activated fractures can generate high proppant concentration and premature blockage of the proppant transport (screen out) (Potluri et al., 2005).

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