Previous Year Question
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?
Abandoned and uneconomic coal seams
Depleted oil and gas reservoirs
Subterranean deep saline formations
Select the correct answer using the code given below:
1 and 2 only
3 only
1 and 3 only
1, 2 and 3
Correct Answer: D
Detailed Solution
Carbon sequestration prevents carbon dioxide from entering the atmosphere and stores it in a suitable natural or geological reservoir for a long period.
In the carbon capture and storage process, CO₂ is separated from an industrial source, compressed and transported through pipelines or other means to a storage site.
Geological storage requires a deep and porous rock layer into which CO₂ can enter and an impermeable caprock above it to prevent the escape of CO₂.
Statement 1 is correct: Carbon dioxide can be stored in abandoned and uneconomic coal seams.
The surface of coal can adsorb carbon dioxide more strongly than methane.
Injecting CO₂ into a coal seam may displace the methane adsorbed there, allowing it to be recovered as an energy source.
This process is associated with enhanced coal-bed methane recovery.
Only deep coal seams unsuitable for mining and having a geological structure that permits safe storage are appropriate.
CO₂ may cause coal to expand or swell, reducing its permeability and making injection difficult.
Statement 2 is correct: Depleted oil and gas reservoirs are potential sites for storing carbon dioxide.
These reservoirs retained oil and gas for millions of years; therefore, the presence of suitable porous rock and an impermeable seal has already been demonstrated.
Comparatively extensive information is available about their geological structure, wells and production history.
Injecting CO₂ into certain oil fields may also help extract the remaining oil, a process known as enhanced oil recovery.
Old or improperly sealed wells may provide pathways for CO₂ leakage, making their examination and sealing necessary.
Statement 3 is correct: Subterranean deep saline formations are considered geological sites with the largest potential capacity for carbon storage.
They contain highly saline water within porous rocks that is generally unsuitable for drinking or irrigation.
When CO₂ is injected at depth, some of it becomes trapped in rock pores, some dissolves in saline water and some may react with minerals over time to form stable carbonates.
Safe storage requires site selection and assessment of leakage, geological pressure, induced seismicity and displacement of saline water.
Therefore, abandoned coal seams, depleted oil and gas reservoirs and deep saline formations are all potential sites for carbon sequestration.