In Situ Studies of “Mineral-CO2” Interactions relevant to Carbon Sequestration

Understanding the chemical/geochemical mechanisms associated with geological sequestration of carbon dioxide, under actual below ground temperatures and pressures, is central to engineering safe and effective long-term storage. However, quantitative data on fluid-solid reactions, fluid-fluid interactions, fluid activities and fluid transport is often difficult to obtain without introducing “quenching effects” associated with the removal of samples from the below-ground setting.  To address this problem we have developed special microreactors which allow systematic laboratory investigation of “rock-CO₂” interactions under in situ sequestration conditions (controlled temperature, pressure, and reactant/solution activity), using x-ray synchrotron diffraction, Raman spectroscopy and NMR. I will describe the outcomes of some recent in situ studies, which reveal that “wet” caprock clay minerals are prone to dehydration and shrinkage in the presence of supercritical CO₂ at fairly moderate conditions. I will also briefly discuss a novel approach to the rapid thermal activation of magnesium-mineral feedstock for applications in ex-situ CO₂ mineralization, in which microreactors are used to efficiently identify improvements in carbonation potential.