A Numerical Hydro-Chemo-Mechanical Model for Fault Activation under Reactive Fluid Flow

Abstract:

The migration of CO₂-rich fluid in fractured rock masses can cause processes such as mineral dissolution and precipitation, chemically induced weakening, which can affect the long-term mechanical and transport properties of the rock mass as well as the stability of fault systems. Some numerical approaches are already available in the literature for modelling the dissolution/precipitation phenomena in fractures (e.g. Yasuhara & Elsworth 2007) as well as subcritical crack propagation (e.g. Park et al. 2007). Generally, the dissolution is supposed to increase the rock porosity and, in this way, decrease the rock strength. Some experimental data are available for the variation of rock strength and stiffness parameters with the porosity and so as a consequence of dissolution process (Bemer et al. 2004). Also the effect of chemical processes on the mechanical stability has been studied and modelled numerically in the framework of continuum materials and the context, in particular, of weathering in underground galleries (Ghabezloo & Pouya 2006). In the context of fault systems, a complete numerical modelling of the stability evolution with the flow of a reactive fluid has not yet been done. In this paper we present a simplified, but complete, set of equations for a whole system of coupled hydro-chemo-mechanical process of reactive fluid flow inside a fault. These equations have been implemented in Porofis, a FEM numerical code specially conceived for HCM processes in porous fractured media. We show how this numerical method allows to model the coupled HCM processes in the fault and the evolution of the mechanical stability in presence of in situ stresses and reactive fluid flow.