In the context of mitigating the impending global warming due to anthropogenic emissions of carbon dioxide, which of the following can be the potential sites for carbon sequestration? Select the correct answer using the code given below:

Answer: (d) 1, 2 and 3

All three are standard geological storage sites.

Statement by statement

1. ✓ YES Unmineable coal seams absorb CO₂ (and release methane that can be used).

2. ✓ YES Depleted oil and gas fields held gas for millions of years — proven traps.

3. ✓ YES Deep saline aquifers have the largest storage capacity.

The idea

A reservoir storage site needs porous rock that can hold the gas and a tight layer above it as a seal. Below about 800 metres the pressure makes CO₂ dense like a liquid, so a lot fits in a small space. Coal seams hold CO₂ on coal surfaces and need not be this deep.

CO₂ is captured at a plant → Compressed and piped → Injected into reservoirs usually deeper than 800 m, or into coal seams → Held in porous rock under a cap rock, or on coal surfaces → In reservoirs, can slowly dissolve and turn into minerals

Also know

Oil and gas fields are proven traps: they held gas for millions of years. Pumping CO₂ into them also pushes out leftover oil (enhanced oil recovery). Coal seams hold CO₂ on the coal surface and release methane that can be used. Deep saline formations have the largest capacity; the first commercial project of this kind was Sleipner in Norway (1996).