Hi Smita, I hope the following is of some help, kind regards, Peter.

Geological sequestration in my article refers to underground storage of carbon dioxide as part of carbon capture, sequestration, and storage (CCSS).

Geological storage means long-term storage in geological formations, natural geological formations such as basalt rock, and saline aquifers, or artificial such as depleted oil and gas fields, and mined coal seams.

Sequestration here means the changing of CO2 into a semi liquid state, under pressure, to keep it within the geological formations.

There is also biological sequestration of carbon in plants by the process of photosynthesis, in the case of plants the sequestration is a chemical change.

The following is quoted from my article

Carbon Capture and Storage from a Point Source | by Peter Miles | Medium

“Carbon dioxide can occur in several states, gas, liquid, solid and supercritical, that is, between a liquid and a gas.

In storage it is pumped to depths of lower than 800metres, the increasing pressure changes CO2 to a supercritical fluid. In this state it can pour into the surrounding porous solid materials.

The increased density of this state also reduces the CO2 buoyancy helping to retain it within the geological formation

Increasing temperatures will drive CO2 to a more gaseous state, so cold, deep sedimentary basins are more suitable for storage.

The mechanisms effect keeping CO2 in deep geological formations after injection are:

The fluid flow of CO2 in the porous material it is injected into and the pressure that holds it in that state.

Fluids flow as a result of natural hydraulic gradients; an example of natural hydraulic gradient is ground water that is at a higher elevation in a nearby hill that will push ground water to the surface in a valley.

Contamination with methane, if storing in disused gas reservoirs, causing the CO2 to be less dense and more buoyant.”