Question

Which geological trapping mechanism involves CO2 dissolving into the brine found within the pores of deep underground rock formations?

Accepted Answer

The geological trapping mechanism involving the dissolution of carbon dioxide into underground brine is called solubility trapping. Deep underground rock formations, known as saline aquifers, contain pore spaces filled with brine, which is water with a high concentration of dissolved salts. When supercritical carbon dioxide—a state where CO2 acts like both a gas and a liquid due to high pressure and temperature—is injected into these formations, it makes contact with the brine. Through the process of diffusion, the carbon dioxide molecules gradually dissolve into the brine, creating a carbonated solution. Because this carbonated brine is slightly denser than the surrounding non-carbonated brine, it tends to sink toward the bottom of the aquifer, which further helps to isolate the carbon dioxide from the surface. This mechanism is crucial for geological carbon storage because it converts the mobile carbon dioxide into a stable, dissolved state within the fluid phase, significantly reducing the risk of the gas migrating back up through the rock layers.

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Which geological trapping mechanism involves CO2 dissolving into the brine found within the pores of deep underground rock formations?