Sub surface storage of CO2 in depleted gas fields in the Netherlands? “No problem” says Suzanne Hangx

The socio-economic impact of global warming resulting from anthropogenic CO₂ emissions has led 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 unmineable coal seams. The former is relevant for countries with an extensive hydrocarbon production and transport infrastructure such as the Netherlands. However, long-term sub surface storage of CO₂ in depleted reservoirs may induce a range of chemical and mechanical processes in response to disturbances in existing chemical equilibria and in the state of stress within the reservoir-cap rock system. Such processes include, but are not limited to, mineralisations reactions, reservoir creep induced by CO₂-water-rock interreactions, and mechanical failure of and permeability development in the seal formations. While some of these processes, such as mineralization, may enhance the CO2 storage capacity of a reservoir, others may potentially reduce reservoir and cap rock integrity, causing leakage of CO₂ tot the geological environment and ultimately to the atmosphere. Today, many of these processes are still poorly constrained.

The work presented in the Thesis focuses on obtaining a fundamental understanding of the effect of CO₂ on mineralization reactions and on time-dependent (i.e. long-term) reservoir compaction or creep phenomena, as well as on cap rock stability and permeability development. The research is 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.