DEM modeling of hydraulic fracturing in fractured shale formation: Effect of inherent anisotropy and induced anisotropy

Hydraulic fracturing has been widely used in the oil and gas industry to increase the recovery of hydrocarbons from low permeability formations. The hydraulic fracturing process can be very complex in naturally fractured reservoirs due to the anisotropy of material properties and existing of natural fractures. The aim of this study is to better understanding the mechanics of hydraulic fracturing in fractured reservoirs by performing numerical simulations in a two-dimensional discrete-element particle flow code (PFC2D). In the numerical model, rock matrix is represented by bonded-particle model (BPM). The intrinsic anisotropy is explicitly represented by imposing smooth-joint models. Any pre-existing horizontal or vertical natural joints are added by superimposing continuous smooth joint contacts onto the BPM to form a Synthetic Rock Mass (SRM) in which fluid injection and rock fracturing can be modeled in a fully coupled manner. The models are first calibrated to reproduce the mechanical behaviors of the isotropic and anisotropic rock in field. Effects of inherent anisotropy, joints orientation, and joint apertures on the hydraulic fracturing growth are investigated by conducting a series of comparative simulations. Results of these simulations showthat the formation’s anisotropy plays an important role in the orientation of hydraulic fractures and it promotes horizontal fracture growth. Joints properties (orientation and aperture) could have a major impact on the behavior of rock mass during hydraulic fracturing operations. © 2016 Taylor & Francis Group, London.