Trapping mechanisms for carbon geosequestration

Trapping mechanisms for carbon geosequestration prevent carbon dioxide stored in geological structures from leaking into the atmosphere. As a means to lower greenhouse gas emissions, carbon dioxide from carbon sequestration, especially in terms of carbon capture and storage, is able to be directed from power plants and other sources of greenhouse gas emissions, with carbon dioxide emissions being pumped into subterranean storage facilities. However, there is still the risk of the carbon dioxide leaking from the underground storage facilities. To address this, several trapping mechanisms have been proposed and researched.

Structural trapping
This is most likely the main solution for preventing leaks. Impermeable (or low permeability) rocks such as caprock or similar material blocks the gas flow. Mudrocks, anhydrite, halite, or tight carbonates are materials that can act as a barrier to the upward buoyant migration of carbon dioxide.

Residual/capillary trapping
Higher capillary forces to buoyant forces cause carbon dioxide to appear as pore-scale bubbles in the formation. This is the is a process through which micrometer scale carbon dioxide bubbles are immobilized by capillary forces within the complex pore structure of the storage rock.

Dissolution trapping
Carbon dioxide dissolves into any water already present in the storage formation. As dissolution proceeds, the water phase density will increase, resulting in downward convective flow of the carbon dioxide saturated water.

Mineral trapping
Chemical reactions between carbon dioxide, water, ions dissolved in the water, and formation minerals can result in carbon dioxide being permanently stored as a solid mineral phase. Examples of rock where this can take place are mafic or ultramafic lithologies.