UPSC Prelims 2017 Q25: Environment & Ecology – Climate Change & Greenhouse Gases
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?
1. Abandoned and uneconomic coal seams
2. Depleted oil and gas reservoirs
3. Subterranean deep saline formations
Select the correct answer
using the code given below:
- (a) 1 and 2 only
- (b) 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Where can CO₂ be stored underground?
Carbon capture and storage (CCS) traps CO₂ and injects it deep underground.
| Site | Suitable? | How it works |
|---|---|---|
| 1. Abandoned and uneconomic coal seams | Yes | CO₂ adsorbs onto coal, and can push out methane (enhanced coal-bed methane) |
| 2. Depleted oil and gas reservoirs | Yes | Proven rock traps; CO₂ injection also aids enhanced oil recovery |
| 3. Deep saline formations | Yes | Largest storage capacity; CO₂ dissolves in salty groundwater |
Storage traps:
| Trap | Mechanism |
|---|---|
| Structural | Cap rock stops CO₂ rising |
| Dissolution | CO₂ dissolves in brine |
| Mineral | CO₂ turns into solid carbonate over time |
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Deep saline formations offer the largest storage capacity of all.
- (b) Incorrect. Coal seams and depleted reservoirs are also proven storage sites.
- (c) Incorrect. Depleted oil and gas reservoirs are among the best-tested CO₂ stores.
- (d) CORRECT. Coal seams, depleted reservoirs and deep saline formations can all store CO₂.
Key point
Geological CO₂ storage: unmineable coal seams (with methane recovery), depleted oil and gas fields (with enhanced oil recovery) and deep saline formations (largest capacity).
Remember
CO₂ storage: coal seams, old oil and gas fields, saline aquifers.
Common mistakes
- Leaving out coal seams, thinking they are only a source of emissions.
- Not knowing saline formations hold the largest potential capacity.
- Forgetting that CO₂ injection can boost oil recovery.
Exam tip
Any deep, sealed rock formation can store CO₂.
Sources
- IPCC — Special Report on Carbon Dioxide Capture and Storage (2005)
- NITI Aayog — CCUS Policy Framework (2022)