Long term CO₂ exposure to brine-saturated chalk; an experimental study

A potential and cost-effective way to reduce the environmental impact of Danish CO₂ emissions would be to store CO₂ in the depleted chalk reservoirs in the North Sea. In this study, we present an investigation of CO₂ long-term exposure into chalk under different in-situ conditions including characterization of the response of chalk dissolution enhancement by CO₂ exposure over time. The experiments are conducted on core material from a specific Danish North Sea reservoir. These core plugs are saturated with representative formation water and then mounted in pressurized cells at an elevated temperature. Supercritical CO₂ is put in contact with the core and brine, and the chemical composition of the brine is monitored. The brine samples are analyzed for Calcium, Magnesium and Sodium, and show the extent of calcite dissolution in the core plugs as well as other minerals being produced as a consequence of CO₂ exposure. These static experiments are presented where brine-saturated core plugs are stored for three months in contact with CO₂ directly and in contact with brine in equilibrium with CO₂. The core material is investigated by CT scanning before and after the experiments to measure the extent of any rock material alteration.