Large scale CO2 storage in unstructured aquifers: Modeling study of the ultimate CO2 migration distance

Abstract

Abstract Design of an industrial scale CO2 geological storage (with a cumulative injection over 50 Mt CO2) into a saline aquifer faces many challenges including the estimation of CO2 storage capacity and injectivity, the assessment of the storage site integrity, the set up of an adequate monitoring program. This paper focuses on another issue related to geological CO2 storage in an unstructured (tilted) aquifer, which is the modeling of the ultimate CO2 lateral migration distance from the injection point. The ultimate CO2 migration distance is difficult to assess as it involves trapping mechanisms associated to different length and time scales. It requires modeling the CO2 dissolution in the aquifer, which can be enhanced as a consequence of the increase of formation water density when CO2 dissolves, resulting in a vertical instability of the water column (convective mixing). Modeling the convective mixing processes requires high resolution grids that are not compatible with aquifer sizes and expected distance of CO2 migration. A numerical approach is presented in order to upscale these processes into the aquifer models. This approach is applied first on a synthetic aquifer model and then on a 200 Mt CO2 storage design into the Mount Simon Sandstone aquifer (USA).