Stress-strain-sorption behaviour and permeability evolution in clay-rich rocks under CO2 storage conditions

Abstract

Carbon Capture and Storage (CCS) is a promising method in the portfolio of negative CO2 emission techniques. It involves capture of CO2 from industrial units (e.g. power plants and cement factories), followed by transport and then injection of the captured CO2 into underground reservoirs, such as saline aquifers, or depleted oil and gas reservoirs, for geological storage. Long-term safe containment of stored CO2 relies on the sealing integrity of the overlying caprock overlying the storage reservoir, as well as any pre-existing faults bounding the system. For many existing and potential CO2 storage sites, clay-rich shales and mudstones form the primary caprock. To assess the leakage risk of CO2 through clay-rich caprocks and along initially sealed faults, the interactions between the caprock material and CO2-rich fluid, and its effect on sealing integrity must be well understood under CO2 storage conditions. In many clay-rich caprocks, swelling clays, such as smectites, are pervasively present. It is known that upon interaction with CO2 and/or water, these clays swell. However, it has not yet been investigated how their swelling behavior impacts caprock and fault integrity under in-situ conditions. This thesis addresses an experimentally-based study on the self-stressing effect in smectite clays induced by volumetric swelling of the smectite due to interactions with CO2 and H2O. Furthermore, it investigates the effect of stress-strain-sorption behaviour of smectites on the transport properties of smectite-bearing shale and fault-filling gouge.