Geological storage of CO₂: Mechanical and chemical effects on host and seal formations

The socio-economic impact of global warming resulting from anthropogenic CO₂ emissions has lead to much attention for carbon mitigation strategies in recent years. One of the most promising ways of disposing of CO₂ is through Carbon Capture and Storage (CCS), entailing CO₂ capture at source, followed by long-term geological storage. Possible storage sites include depleted oil and gas reservoirs, saline aquifers and unminable coal seams. The former is relevant for countries with an extensive hydrocarbon production and transport infrastructure, such as the Netherlands. However, long-term subsurface storage of CO₂ in depleted reservoirs may induce a range of chemical and mechanical processes in response to of disturbances in existing chemical equilibria and in the state of stress within the reservoir-caprock system. Such processes include, but are not limited to, mineralisation reactions, reservoir creep induced by CO₂-water-rock interactions, and mechanical failure of and permeability development in the seal formation. While some of these processes, such as mineralisation, may enhance the CO₂ storage capacity of a reservoir, others may potentially reduce reservoir and caprock integrity, causing leakage of CO₂ to the geological environment and ultimately to the atmosphere. To date, many of these processes are still poorly constrained. The work presented in this thesis focuses on obtaining a fundamental understanding of the effect of CO₂ on mineralisation reactions and on time-dependent (i.e. long-term) reservoir compaction or creep phenomena, as well as on caprock stability and permeability development. As the project formed part of the Dutch National Research Program CATO, on CO₂ capture, transport and storage, it has been directed at reaction and deformation effects in sandstone and anhydrite, which are the main rock types representing potential host and seal formations for subsurface CO₂ storage in the Netherlands. In response to much media attention for the concept of CO₂ removal from the atmosphere by (coastal) weathering of imported, sand-grade olivine, the feasibility of this concept has also been assessed.