Geochemical impact of CO2 and H2 injection on geomechanical and petrophysical properties of caprock to ensure safe containment: an experimental and an

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CO2 and H2 storage developers have a moral, social, and legal responsibility to ensure safe containment over geological time scales. Critical to safe and predictable long-term storage of CO2 and H2 within geological media, is the need to understand caprock behaviour in the presence of potentially reactive fluids. Injection of CO2 and H2 for storage into saline aquifers and/or depleted hydrocarbon reservoirs will alter the in-situ geochemical environment, potentially leading to reactions with the caprock. This, in turn, may alter the geomechanical and petrophysical properties of the caprock, possibly increasing the risk of migration out of the host reservoir. The coupled geochemical and geomechanical effects on caprocks in the presence CO2 or H2 are poorly understood and under-researched despite being key controls on rock strength and sealing capacity. By investigating the interplay between these two disciplines, a new understanding on controllers of rock strength and subsequent leakage pathways can be constrained, helping de-risk future CCUS and potential H2 storage projects. This pioneering experimental study will directly reveal the geochemical effects on key geomechanical properties of caprocks under representative reservoir conditions. Measurements of how the strength, permeability, elastic and acoustic properties, and reactive surface area of caprocks are affected by the presence of injected fluids will provide fundamental constraints on caprock integrity for CO2 and H2 injection sites. This work will enable identification of the unique geochemical and geomechanical differences between CO2 and H2 injection upon key caprock properties, the first comparison study of its kind, aiding future site selection by providing criteria to differentiate and rank sites by the long-term stability of the caprock.