Chemical reactions at fluid-shale interfaces, such as mineral precipitation or carbonate dissolution, occur at multiple scales and may induce significant changes in transport properties of the bulk rock. It is also expected that local stress gradients and preexisting, geological non-bedding microstructural heterogeneities (such as the presence of relatively incompressible mineral grains) exert significant control over transport and chemical reaction progress. Thus, reaction fronts marking sharp gradients in pH, mineral solubility, redox conditions, or other fluid-solid interactions develop at grain boundaries, microcrack interfaces and/or local heterogeneities, as well as at fracture network scales and influence ultimately the overall evolution of rock properties (transport and mechanical). This coupled evolution is critical to understanding and manipulating reactivity and transport properties of shale-fluid interfaces for ends such as improved hydrocarbon production efficiency, improved reactive flow of hydrothermal fluids, and controlled adsorption/desorption of cations, anions, and molecules.
This discussion emphasizes the importance of understanding coupling between microcracks, fluid transport, and chemical/mechanical shale alteration. Simple scaling models and current numerical models cannot predict the evolution of shale-fluid interfaces over time, yet this parameter partly controls the behavior of the rock over timescales from days to decades. In addition to transport rates, we propose to explore two critical parameters: (i) the nature of the reaction network that controls the kinetics and (ii) the opening (or closing) of porosity and exposure (or occlusion) of surface area at the reaction fronts.