A calculation model for liquid CO₂ injection into shallow sub-seabed aquifer

This study provided a model for calculating the aquifer transmissibility, the CO₂ injection rate, the inner diameter of the injection well, and the number of wells for liquid CO₂ disposal in the aquifer. The possibility of disposing liquid CO₂ in an aquifer just beneath the sea floor was shown, based on the equilibrium lines in the pressure and temperature map. Our study focused on the feasibility of liquid CO₂ disposal below the critical temperature because CO₂ can be denser in the low-pressure range (below the critical temperature) than above the critical temperature. An aquifer about 200 m under the sea floor, at a water depth of around 500 m (700 m below the sea surface), will serve for liquid CO₂ disposal. In the aquifer the absolute pressure is approximately 7.3 MPa, sea-floor temperature is about 4-6°C, and aquifer temperature is about 15-20°C. Therefore, it can be assumed that CO₂ dissolves in the aquifer water, and liquid CO₂ replaces the water. This means that under the previous conditions, more CO₂ can be injected into the aquifer compared to supercritical conditions. Furthermore, by forming a cap of CO₂ hydrates, the sediment between the sea floor and the aquifer, prevents CO₂ leakage to the sea. Even without the cap, liquid CO₂ and CO₂ hydrates form at the sea floor, so the CO₂ exerts no large environmental impact.