Abstract
In gas and oil as well as in several mining applications hydro-mechanical phenomena play an important role and need to be considered in numerical models for calibration and forecasting analyses. In this paper, a two-way coupled hydromechanical formulation is described and applied to real size, complex 3D mining and reservoir model examples including structures using the Finite-Element Method (FEM) framework. The proposed coupling considers increasing hydraulic conductivities due to the evolution of rock mass damage induced by mining activities or fluid injection. This enables the potential development of additional flow paths and affects the fluid pressure distribution, which, in turn, affects the mechanical response via the effective stress concept. The mechanical framework uses a strain-softening, dilatant and discontinuum constitutive model for both bulk rockmass and structures such as faults on a regional scale and discrete fracture networks (DFN).
1. INTRODUCTION
Hydro-mechanical phenomena for geotechnical extraction applications, as in the mining or gas and oil industries, are very important aspects of global or well stability, subsidence and in some cases, accurate forecasting of recovery. Most adverse rock related hydro-mechanical phenomena are stress path dependent. Uncoupled or loosely coupled modelling of flow or rock deformation is therefore not ideal; the important fluid rock coupling is over-simplified, or else, the stress path may not be replicated with high similitude.
Here, we present closely and fully coupled, parallel solution formulation adopting single and multi-phase, multi-component fluid flow formulations into a discontinuum, strain softening, and dilatant Finite Element model. Particular emphasis is on the nonlinear coupling of the deformable and strain softening solid skeleton and the fluid phase(s), e.g. the change of hydraulic properties with evolution of damage in the matrix material as well as the effect of pore pressures on the overall stress distribution. This governing system of coupled nonlinear partial differential equations is embedded in the framework of a Finite-Element (FE) algorithm and applied to various large-scale real-life mine and reservoir models.
