A Micromechanical Model for Mineral Replacement Reactions and Associated Deformation: From Pore Clogging to Solid Volume Increase

Deformation, chemical reactions, and fluid flow in geological formations are coupled processes. Recent experimental and observational studies suggest that mineral replacement is typically driven by coupled dissolution–precipitation processes, often leading to variable changes in porosity and solid volume depending on the specific reaction conditions. This article builds upon our previous micromechanical model for mineral replacement reactions and the associated deformation processes. Our new model accommodates externally applied stresses and stresses generated as a result of chemical reactions through elastic, viscous, and plastic deformation mechanisms. Our model predicts changes in both porosity and solid volume as a result of the chemical reaction, with these changes governed by the relative rates of deformation of the solid and pore volumes. Porosity reduction often limits the extent of the reaction, while solid volume increase, accompanied by a lesser reduction in porosity, facilitates achieving complete reactions. An interesting finding of our model is the emergence of two solid bulk moduli, typically associated with the presence of a non-connected pore space. However, in our case, they are associated with chemical alterations. We also introduce an effective stress law for reactive porous rocks. We use a two-phase continuum medium approach and local equilibrium thermodynamic models to investigate the coupling between reaction, deformation, and fluid flow on a larger scale. This framework offers valuable insights into the complex interplay between geological processes and the mechanical behavior of rocks undergoing mineral replacement reactions, with implications for understanding subsurface fluid flow and the evolution of geological formations.