Techno-economic assessment of supercritical, cold liquid, and dissolved CO2 injection into sub-seafloor basalt

Injecting CO₂ into subsea basalt can provide permanent storage via multiple trapping mechanisms, including mineralization reactions which convert the CO₂ into solid carbonates over time. Injecting CO₂ together with water can accelerate the process of mineralization, but presents additional challenges, such as high energy and water requirements. A techno-economic model of CO₂ transport and injection into ocean basalt was developed to compare injection strategies using pure supercritical CO₂, pure liquid CO₂, and CO₂ dissolved in seawater. The model was applied to a representative injection site off the coast of British Columbia, Canada. Injection of CO₂ dissolved into seawater was found to be more energy and cost intensive than injection of supercritical or liquid CO₂; this is primarily due to the reduced quantities of CO₂ that can be injected into each well, and additional pumping energy required for the accompanying seawater. For the base assumptions, transport and storage costs for supercritical, liquid, and dissolved injection were estimated as $43/t, $38/t, and $250/t respectively. Their energy requirements were estimated as 93 kWh/t, 90 kWh/t, and 213 kWh/t respectively. The current best estimates of geological parameters for ocean basalt suggest good injectivity and very large storage capacities per well. This may help to compensate for the additional project expenses incurred by deep water, allowing cost-effective liquid and supercritical injection. However, this result is sensitive to high uncertainties in both geological parameters and component cost data.