Pore-Space Alteration Induced by Brine Acidification in Subsurface Geologic Formations

A new Lagrangian particle-based method is presented to simulate reactive transport in natural porous media. This technique is based on Modified Moving Particle Semi-implicit (MMPS) and takes as input high-resolution voxel images of natural porous media. The flow field in the medium is computed by solving the incompressible Navier-Stokes equations. Moreover, a multicomponent ion transport model is coupled with a homogeneous and heterogeneous reactions module to handle pore-space alteration (i.e., pore-wall dissolution). The model is first successfully validated against the experimental data available in the literature. Subsequently, X-ray microtomographic images of two naturally occurring porous media are used to investigate the impact of reaction kinetics and pore-space topology on pore-space alteration induced by brine acidification in subsurface conditions. We observed that at the normal rates of reactions no significant change in porosity and permeability takes place in the short term. Whereas, higher reaction rates caused major changes in the macroscopic properties (e.g., porosity and permeability) of the rocks. We also show that these changes are strongly affected by the rocks' pore-scale topologies. Key points: A direct pore-scale model is developed to simulate rock/fluid chemical reactions Chemical alteration of pore space leads to significant changes in permeability Pore-space topology determines the extent of change in permeability and porosity.