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Modeling Stimulated Rock Volumes Using DPDK Approach Coupled With Rock Mechanics


A stimulation design involves a comprehensive engineering design procedure, which takes into account of formation evaluation, fracturing fluid characterization, proppant transportation, rock mechanics, and ultimate stimulated reservoir volume (SRV) approximation through 3D fracture propagation modeling. The ultimate recovery is mainly controlled by fracture conductivity and SRV (Gidley et al., 1990), which are the key indicators to a stimulation success. Because of ultra-tight rock matrix permeability in a Nano-Darcy range for Tight Oil and Liquid Rich condensate reservoirs, propped fracture channels or a complex fracture network must maintain enough conductivity to achieve an economic production rate. Lab experiments using an API procedure showed that the fracture conductivity dropped several orders of magnitudes under the loading condition for various commercial fracturing proppants (Fredd et al. 2001). Therefore, modeling the fracture conductivity degradation vs. increasing of net effective stress becomes a critical issue for a long term production forecast. Modeling a hydraulically fractured unconventional tight sand reservoir is a coupled hydro-mechanical problem associated with complex interactions between dynamical fracture deformation under a loading condition and multiphase flow inside a fracture network. In this paper, a DPDK model with numerical MINC (multiple interacting continua) algorithms is utilized to represent the pressure transient within the tight matrix and interporosity flow from the matrix into a hybrid system consisting of a complex fracture network. The flow model is coupled with a FEM stress code to model the dynamical changing of fracture aperture associated with increasing of the effective normal stress during the pressure depletion. In addition, the choice of a coupling approach is critical because of the slow nonlinear convergence due to a significant increase in unknowns associated with poroelasticity equations. In this paper, the iterative coupling is adopted to solve the multiphase flow and stress equations using parallel computations because of its flexibility and efficiency compared to the fully coupled approach. A hydraulic fracture deformation mechanical model is developed and implemented into the PRSI framework. The fracture network closure is approximated by the Barton-Bandis hyperbolic deformation model, coupled with a modified Cubic Law based on a contact theory and validated by an API proppant test on proppant conductivity under loading stress. Finally, numerical examples on hydraulic fracture deformation will be presented. The coupled fluid flow-rock mechanics will illustrate the degradation of the fracture conductivity due to the increasing of normal stresses for a variety of proppant types.