Status of CO₂storage in deep saline aquifers with emphasis on modeling approaches and practical simulations

TLDR

Carbon capture and storage, especially injection into deep saline aquifers, is the only viable technology to mitigate emissions while allowing continued fossil fuel use, and although the resulting multiphase flow system is complex, its physics can sometimes be simplified. Because the large density contrast between CO₂ and brine drives rapid buoyant segregation, a vertical‑equilibrium assumption often holds, enabling simplified models that, when calibrated with field data, clarify system behavior. These simplified models provide practical estimates of storage capacity, CO₂ migration, pressure response, and leakage risk, demonstrating that deep saline aquifer storage is a viable climate‑change solution despite remaining economic and policy challenges.

Abstract

Carbon capture and storage (CCS) is the only viable technology to mitigate carbon emissions while allowing continued large-scale use of fossil fuels. The storage part of CCS involves injection of carbon dioxide, captured from large stationary sources, into deep geological formations. Deep saline aquifers have the largest identified storage potential, with estimated storage capacity sufficient to store emissions from large stationary sources for at least a century. This makes CCS a potentially important bridging technology in the transition to carbon-free energy sources. Injection of CO2 into deep saline aquifers leads to a multicomponent, multiphase flow system, in which geomechanics, geochemistry, and nonisothermal effects may be important. While the general system can be highly complex and involve many coupled, nonlinear partial differential equations, the underlying physics can sometimes lead to important simplifications. For example, the large density difference between injected CO2 and brine may lead to relatively fast buoyant segregation, making an assumption of vertical equilibrium reasonable. Such simplifying assumptions lead to a range of simplified governing equations whose solutions have provided significant practical insights into system behavior, including improved estimates of storage capacity, easy-to-compute estimates of CO2 spatial migration and pressure response, and quantitative estimates of leakage risk. When these modeling studies are coupled with observations from well-characterized injection operations, understanding of the overall system behavior is enhanced significantly. This improved understanding shows that, while economic and policy challenges remain, CO2 storage in deep saline aquifers appears to be a viable technology and can contribute substantially to climate change solutions.