Abstract Extraction or injection of fluids within the subsurface causes fluctuations of fluid pressures and thus stress conditions. It is paramount to have knowledge of the geomechanical strength of a system’s lithologies, and the factors that control it, in order to maintain optimal conditions during extraction/injection. If the yield strengths of the reservoir or caprock are overcome, particularly in the near-wellbore region where stress is amplified, these fluctuations could potentially compromise the system, through compactional or dilatational failure. Here we have used a novel combination of methods to determine the geomechanical and petrographic properties of the reservoir and caprock lithologies to assess suitability of the proposed Acorn CO2 Storage Site, offshore north-east Scotland, for long-term injection and storage of CO2. The Acorn CO2 Storage Site has a highly porous and transmissible sandstone reservoir, with bulk mineralogy that will be stable under CO2-rich conditions, making it ideal for receiving at least 152 MT CO2 injected over ∼ 20 years and storage of > 1000 years post-injection, as part of the ACT-Acorn Development Plan. However, due to the high porosity and low cementation of the sandstone reservoir, it has low yield strength and is vulnerable to disaggregation and porosity-reduction if injection rates are too high and stress/pressure conditions exceed their yield strength. The results presented here provide quantitative constraints on the porosity reduction expected should yield occur and place li...
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