An embedded fracture modeling framework for simulation of hydraulic fracturing and shear stimulation

Abstract

A numerical modeling framework is described that is able to calculate the coupled processes of fluid flow, geomechanics, and rock failure for application to general engineering problems related to reservoir stimulation, including hydraulic fracturing and shear stimulation. The numerical formulation employs the use of an embedded fracture modeling approach, which provides several advantages over more traditional methods in terms of computational complexity and efficiency. Specifically, the embedded fracture modeling strategy avoids the usual requirement that the discretization of the fracture domain conforms to the discretization of the rock volume surrounding the fractures. As fluid is exchanged between the two domains, conservation of mass is guaranteed through a coupling term that appears as a simple source term in the governing mass balance equations. In this manner, as new tensile fractures nucleate and propagate subject to mechanical effects, numerical complexities associated with the introduction of new fracture control volumes are largely negated. In addition, the ability to discretize the fractures and surrounding rock volume independently provides the freedom to choose an acceptable level of discretization for each domain separately. Three numerical examples were performed to demonstrate the utility of the embedded fracture model for application to problems involving fluid flow, mechanical deformation, and rock failure. The results of the numerical examples confirm that the embedded fracture model was able to capture accurately the complex and nonlinear evolution of reservoir permeability as new fractures propagate through the reservoir and as fractures fail in shear.

Evidence for a transient hydromechanical and frictional faulting response during the 2011 Mw 5.6 Prague, Oklahoma earthquake sequence

“…For one‐dimensional Darcy flow in the along‐fault direction, fluid mass balance can be expressed as [ Norbeck et al , ] where T is fault transmissivity, ρ is water density, μ is water viscosity, and E is fault void aperture. The fault transmissivity can be thought of as the product of permeability and hydraulic aperture (thickness available for flow in the along‐fault direction).…”

“…For one-dimensional Darcy flow in the along-fault direction, fluid mass balance can be expressed as [Norbeck et al, 2016a] x…”

A finite-volume discretization for deformation of fractured media

“…In the literature on computational analysis of fractured domains, two main approaches have been applied: the boundary-element method (BEM) and the finite-element method (FEM) [7,8]. The BEM has been effectively applied to fracture problems for the past several decades, and its area of application has recently widened [3,[9][10][11][12][13]. The BEM can accommodate problems including nonhomogeneous materials using Green's functions [9] and can be extended to 3D simulations [14].…”

Re-examining interpretations of non-ideal behavior during diagnostic fracture injection tests

“…In the 2D simulations for this study, fluid leakoff is calculated fully numerically with a conforming triangular mesh (Norbeck et al, 2015). In the 3D simulations, leakoff is calculated with the one-dimensional leakoff model introduced by Vinsome and Westerveld (1980).…”