Abstract:
This paper presents the development, verification and application of a new, fully-coupled, hydro-mechanical (HM) formulation for a finite-discrete element method (FDEM) software package called Irazu. FDEM is a general-purpose numerical approach which combines continuum mechanics principles with discrete element algorithms to simulate the mechanical response of brittle geomaterials. In the newly-developed, integrated hydraulic solver, fluid flow is assumed to occur through a network generated from the same triangular mesh used for the mechanical calculations. The flow of a viscous, compressible fluid is explicitly solved based on a cubic law approximation. The modeling approach is applied to the field-scale simulation of fluid injection in a jointed and porous rock mass. Results show that the proposed numerical approach can be used to obtain unique geomechanical insights into coupled HM phenomena, including fluid-driven fracturing in permeable rocks and interaction between induced and natural fractures.
Introduction
The interaction between hydraulic and mechanical processes in rock masses is commonly known as hydromechanical (HM) coupling. Rock masses consist of a porous matrix with embedded discontinuities, including joints, faults, bedding planes, and anthropogenic fractures. In general, it is possible for fluids to fill and flow through the permeable matrix, the existing discontinuity network, and any new fractures that may be generated by hydraulic and mechanical loading. Mathematical descriptions of the rock mass HM behavior should therefore consider the coupled response of all the above components. Theoretical and computer simulation advances in coupled HM processes have been driven by several geomechanical applications in rock engineering (e.g., stability of underground and surface excavations), underground nuclear waste disposal (e.g., design and performance assessment of geological repositories), exploration and production of hydrocarbons (e.g., hydraulic fracturing), extraction of geothermal energy (e.g., enhanced geothermal systems), and mining (e.g., coal methane extraction).
The goal of this paper is to present the preliminary results of a research effort aimed to develop and validate an HM formulation for the hybrid finite-discrete element method (FDEM). FDEM is a general-purpose numerical approach which combines continuum mechanics principles, such as theory of elasticity and non-linear elastic fracture mechanics, with discrete element algorithms to simulate multiple interacting, deformable, and fracturable solids (Mahabadi et al., 2012). In recent years, it has been used for a variety of rock mechanics problems where an explicit consideration of fracture nucleation and growth is of paramount importance (Mahabadi et al., 2014, Tatone and Grasselli, 2015, Lisjak et al., 2015). The new HM formulation was implemented in the FDEM software of Geomechanica Inc. named Irazu (Geomechanica Inc., 2016). Irazu is an innovative simulation package that leverages the parallel processing power of general-purpose graphics processing units (GPGPUs) to gain significant performance boosts compared to existing sequential FDEM codes (Mahabadi et al., 2016).
