Shear and vertical deformation behaviour at the field scale during CO₂ storage in a depleted chalk reservoir (Danish North Sea)

CO₂ storage represents one of the recommended remediation methods to reduce the emission of anthropogenic CO₂ in the atmosphere. As part of the Bifrost project that aims at developing CO₂ storage activities in Denmark, a series of coupled hydro-mechanical-chemical simulations is carried out in the Harald East chalk field to assess the flow and mechanical response of the storage site, assuming both continuous and intermittent injection. A total of two continuous injection scenarios during 16 years (scenario 1) and 32 years (scenario 2) and scenario 3 which assumes intermittent injection are considered. The injection rate in scenario 2 and 3 is half of that of scenario 1, and the duration of the injection in scenario 3 is increased compared to scenario 1. The rate and duration of injection are adjusted to ensure a similar volume of stored gas in each simulation run. The outcomes show that fast injection prevents significant compaction in the reservoir. Besides, the calculated shear deformation in the overburden is utilised to study wellbore stability during storage. The results indicate that the accurate characterisation of the porosity distribution in the reservoir as well as the potential mechanical weakening of chalk by CO₂ are essential for reliable wellbore integrity analyses. Further studies will be conducted to assess wellbore stability in the Harald East area during CO₂ storage activities.