Convective mixing fingers and chemistry interaction in carbon storage

Dissolution of carbon-dioxide into formation fluids during carbon capture and storage (CCS) can generate an instability with a denser CO2-rich fluid located above the less dense native aquifer fluid. This instability promotes convective mixing, enhancing CO2 dissolution and favouring the storage safety. Convective mixing has been extensively analysed in the context of CCS over the last decade, however the interaction between convective mixing and geochemistry has been insufficiently addressed. This relation is explored using a fully coupled model taking into account the porosity and permeability variations due to dissolution-precipitation reactions in a realistic geochemical system based on the Hontomín (Spain) potential CCS site project. This system, located in a calcite, dolomite, and gypsum bearing host rock, has been analysed for a variety of Rayleigh and Damköhler values. Results show that chemical reactions tend to enhance CO2 dissolution. The model illustrates the first stages of porosity channel development, demonstrating the significance of fluid mixing in the development of porosity patterns. The influence of non-carbon species on CO2 dissolution shown in this study demonstrates the needs for realistic chemical and kinetic models to ensure the precision of physical models to accurately represent the carbon-dioxide injection process.