A test of the effectiveness of pore scale fluid flow simulations and constitutive equations for modelling the effects of mineral dissolution on rock permeability

Macro-scale transport properties of rocks such as permeability are bulk parameters combining the contributions of various properties only properly defined at the pore scale. Since pore-scale processes are known to modify the rock properties it is legitimate to ask if constitutive equations based on macro scale properties (e.g. porosity, permeability, formation factor, etc…) can properly describe their effect. In a previous experimental study (Lamy-Chappuis et al., 2014) we found that the effect of mineral dissolution on permeability could be much higher than predicted by such semi-empirical constitutive equations. Here we directly solve pore-scale fluid flow in high-resolution (2.5 μm) 3D models of a rock's geometry before and after mineral dissolution in order to evaluate permeability and how it is changed. This methodology is limited by the resolution of the micro-CT images used to define the rock geometry, which leads to significant overestimates of absolute permeability, but it does produce a much closer match to the change in permeability due to mineral dissolution than the constitutive equations. This is possible because the dissolution features, which enhance permeability, are large enough to be adequately resolved and produce a significant change in permeability.