ALL ABOUT CARBON DIOXIDE

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CO2 is made of one carbon and two oxygen atoms. It occurs naturally as part of the earth’s system in both the atmosphere and underground. CO2 can be found in many products that consumers use every day. For example, CO2 is what makes soft drinks fizzy and is used in pain relievers, such as Alka-Seltzer. CO2 can be found in fire extinguishers or in solid form, more commonly known as dry ice. The chemical properties of CO2 are inherently stable, so it is not considered to be a detriment to humans or the environment in regulated quantities. Geological sequestration can act as a shortcut in the carbon cycle by bypassing the atmosphere and injecting it directly into the ground.

SUPERCRITICAL CO2
CO2 is injected below 2500 feet to ensure it is in super critical form. Supercritical fluids take up less space than gases and can also spread more easily into tiny pore spaces in the rock. This figure shows how the volume of CO2 at the surface is much bigger than the volume of the same amount of CO2 under supercritical conditions.



WHERE CAN CO2 BE SEQUESTERED?
CO2 can be sequestered in deep underground formations of porous and permeable rock. To be suitable for CCS, porous and permeable formations must lie underneath layers of impermeable rock that will provide a “cap” or seal to prevent upward migration of the CO2. Geologists look for rock formations below 2500 ft (800 m) in order to meet the pressure and temperature requirements for supercritical CO2.




CO2 PLUME MIGRATION AND TRAPPING MECHANISMS
Once CO2 is injected into a deep underground formation, it is confined in tiny pore spaces within the rock layer. Subsurface temperature and pressure keep sequestered CO2 in a supercritical state. Impermeable rock units, or cap rocks, serve as barriers against migration of the CO2 toward the surface. Over time, the CO2 becomes even more securely trapped as it dissolves into the salty water of a saline formation or undergoes natural reactions to form a solid mineral. Ongoing geologic research has demonstrated that the risk of CO2 finding its way back to the surface is extremely low.

Plume Migration

 


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