In the context of mitigating the impending global warming due to anthropogenic emissions of carbon dioxide, which of the following can be 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:
Contents24
- A1 and 2 only
- B3 only
- C1 and 3 only
- D1, 2 and 3
Show answer
Answer: (D) 1, 2 and 3
All three are potential sites for geological carbon sequestration.
Carbon sequestration refers to the process of capturing atmospheric CO2 and storing it long-term to mitigate global warming.
Geological sequestration involves injecting captured CO2 deep underground into suitable rock formations where it is trapped and stored permanently.
The three main types of geological storage sites are:
(1) Abandoned and uneconomic coal seams: CO2 can be injected into coal seams that are too deep or thin to be economically mined. The coal surface adsorbs (binds) CO2 molecules, trapping them. An additional benefit is that injecting CO2 can displace methane trapped in the coal, which can then be recovered and used as fuel — this is called Enhanced Coal Bed Methane (ECBM) recovery.
(2) Depleted oil and gas reservoirs: These are geological formations that previously held oil or gas for millions of years, proving they can trap fluids effectively. Once the oil/gas is extracted, the empty pore spaces can be filled with CO2. Injecting CO2 can also help extract remaining oil — this is called Enhanced Oil Recovery (EOR).
(3) Subterranean deep saline formations: These are deep underground layers of porous rock saturated with brine (salty water). They have the largest potential storage capacity among all geological options. CO2 injected into these formations dissolves in the brine or gets trapped in the rock pores.
All three sites are well-established in carbon capture and storage (CCS) science.
So statements 1, 2, and 3 are all correct.
Carbon capture and storage (CCS) technology is essential for meeting global climate targets, as it can potentially store billions of tons of CO2 underground in geological formations.
The 2015 Paris Agreement created international focus on carbon sequestration technologies, making CCS a key topic in climate policy discussions around 2017.
UPSC is testing whether students understand that carbon storage works by using the same geological principles that trapped oil, gas, and methane for millions of years.
Geological Carbon Sequestration
Environment carbon sequestration abandoned coal seams depleted oil and gas reservoirs deep saline formations
Geological Carbon Sequestration: Storage Sites & Mechanisms
Quick Recall
All three sites (coal seams, oil/gas reservoirs, saline formations) are viable for CO2 storage
Deep saline formations have the largest storage capacity globally
Enhanced recovery - CO2 injection can extract remaining oil (EOR) or methane (ECBM)
CO2 is stored through adsorption (coal), pore filling (reservoirs), or dissolution (saline)
What is Geological Sequestration
Geological carbon sequestration involves capturing atmospheric CO2 and injecting it deep underground into suitable rock formations for permanent storage. This is a key climate mitigation technology that prevents CO2 from reaching the atmosphere and contributing to global warming.
Three Main Storage Sites
Storage Site | Storage Mechanism | Additional Benefit | Key Requirement |
|---|---|---|---|
Abandoned Coal Seams | CO2 adsorbs onto coal surface | ECBM - methane recovery | Too deep/thin to mine economically |
Depleted Oil/Gas Reservoirs | CO2 fills empty pore spaces | EOR - enhanced oil recovery | Proven trap integrity over millions of years |
Deep Saline Formations | CO2 dissolves in brine or fills pores | Largest capacity globally | Deep underground brine-saturated rock |
Storage Mechanisms
Structural trapping - CO2 trapped under impermeable cap rock layers
Residual trapping - CO2 droplets trapped in tiny rock pores by surface tension
Solubility trapping - CO2 dissolves into formation water (brine)
Mineral trapping - CO2 reacts with rock minerals to form stable carbonates (long-term)
Question Context
This 2017 UPSC question tested knowledge of all three geological storage options. The trap was thinking only some sites work - but all statements 1, 2, and 3 are correct, making option D the answer.
All three sites work - don't eliminate any storage option as 'impossible'
Deep saline formations are the most promising (largest capacity), but others are also viable
Enhanced recovery is a bonus benefit, not a requirement for storage
Don't confuse adsorption (surface binding) with absorption (internal uptake)
Carbon Capture & Storage Technology
Environment carbon dioxide anthropogenic emissions global warming
Carbon Capture & Storage (CCS): Technology & Process
CCS Essentials
CCS captures CO2 from emission sources and stores it permanently underground
Three steps: Capture → Transport → Storage in geological formations
Can capture 85-95% of CO2 emissions from power plants and industries
Post-combustion capture is most common for existing facilities
CCS Overview
Carbon Capture and Storage (CCS) is a climate technology that prevents large quantities of CO2 from being released into the atmosphere. It captures CO2 from major emission sources like power plants and industrial facilities, then transports and stores it safely underground.
CCS Process Chain
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**CO2 Capture**
Extract CO2 from flue gases at power plants, cement factories, steel mills`"]
s2["`**CO2 Compression**
Compress captured CO2 into liquid/supercritical state for transport`"]
s3["`**CO2 Transport**
Move compressed CO2 via pipelines, ships, or trucks to storage site`"]
s4["`**CO2 Injection**
Inject CO2 deep underground into suitable geological formations`"]
s5["`**Monitoring**
Continuously monitor storage site to ensure CO2 remains trapped`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Capture Technologies
Capture Method | When Used | Efficiency | Key Feature |
|---|---|---|---|
Post-combustion | Existing power plants | 85-95% | Captures CO2 from flue gas after burning |
Pre-combustion | New gasification plants | 85-95% | Removes CO2 before fuel combustion |
Oxy-fuel combustion | Specialized new plants | 90%+ | Burns fuel in pure oxygen, produces concentrated CO2 |
Global CCS Status
Norway - Sleipner project storing 1 million tonnes CO2/year since 1996
Canada - Boundary Dam power plant, world's first commercial CCS on coal
India - ONGC exploring CCS for oil fields, pilot projects in planning
IPCC estimates - CCS needed for 14% of global emission reductions by 2050
CCS ≠ Carbon offsetting - CCS is permanent geological storage, not planting trees
All fossil fuels can use CCS - not limited to coal power plants
Transport costs are significant - storage sites must be reasonably close to sources
Monitoring required - must verify CO2 stays underground permanently
Enhanced Oil & Gas Recovery
Environment depleted oil and gas reservoirs
Enhanced Recovery: EOR & ECBM with CO2 Injection
Enhanced Recovery Basics
EOR uses CO2 to extract remaining oil from depleted reservoirs
ECBM uses CO2 to displace methane from uneconomic coal seams
Both provide economic incentive for CCS projects by generating revenue
CO2 remains permanently stored after enhancing recovery
Win-Win Technology
Enhanced recovery techniques use CO2 injection to extract additional fossil fuels from formations while permanently storing the CO2. This creates economic value that helps offset CCS costs, making carbon storage projects more financially viable.
EOR vs ECBM Comparison
Technique | Target Formation | Recovered Product | CO2 Role | Storage Benefit |
|---|---|---|---|---|
Enhanced Oil Recovery (EOR) | Depleted oil reservoirs | Remaining crude oil | Reduces oil viscosity, maintains pressure | CO2 stays trapped in reservoir |
Enhanced Coal Bed Methane (ECBM) | Deep uneconomic coal seams | Methane gas | Displaces methane from coal surface | CO2 adsorbs onto coal permanently |
Technical Mechanisms
EOR process - CO2 mixes with oil, reducing viscosity and making it flow easier
ECBM process - CO2 has higher affinity for coal than methane, displacing CH₄
Miscible flooding - CO2 dissolves completely in oil at high pressure
Immiscible flooding - CO2 pushes oil toward production wells without mixing
EOR Process Steps
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Primary Recovery**
Natural pressure extracts 10-20% of original oil`"]
s2["`**Secondary Recovery**
Water/gas injection extracts additional 20-40%`"]
s3["`**Tertiary Recovery (EOR)**
CO2 injection extracts remaining 5-15% of oil`"]
s4["`**Permanent Storage**
Injected CO2 remains trapped in depleted reservoir`"]
s1 --> s2
s2 --> s3
s3 --> s4EOR is tertiary recovery - comes after primary and secondary extraction methods
Both techniques store CO2 - they're not just about fuel extraction
Economic viability depends on oil/gas prices making recovery profitable
ECBM works on deep coal - not surface mining or shallow seams
Climate Mitigation Technologies
Environment mitigating global warming anthropogenic emissions
Climate Mitigation: Technologies & Strategies for Emission Reduction
Mitigation Essentials
Mitigation reduces greenhouse gas emissions or enhances carbon sinks
CCS is one strategy - others include renewables, efficiency, afforestation
IPCC target: 45% emission reduction by 2030, net-zero by 2050
Technology + policy both needed for effective climate action
Mitigation vs Adaptation
Climate mitigation focuses on reducing the causes of climate change by cutting greenhouse gas emissions or removing CO2 from the atmosphere. This differs from climate adaptation, which focuses on adjusting to climate change impacts that are already occurring.
Mitigation Technology Categories
# Climate Mitigation Technologies
## Energy Supply
- Renewable Energy
- Nuclear Power
- CCS for Fossil Plants
- Energy Efficiency
## Transport
- Electric Vehicles
- Biofuels
- Hydrogen Fuel
- Public Transit
## Industry
- Process Efficiency
- Material Substitution
- Industrial CCS
- Circular Economy
## Carbon Removal
- Afforestation
- BECCS
- Direct Air Capture
- Soil CarbonEmission Reduction Potential
Mitigation Option | Sector | 2030 Potential (GtCO2/yr) | Key Technologies |
|---|---|---|---|
Renewable Energy | Electricity | 7-12 | Solar, Wind, Hydro, Geothermal |
Energy Efficiency | Buildings/Industry | 5-10 | LED, Insulation, Heat Pumps, Motors |
Transport | Mobility | 2-5 | Electric Vehicles, Biofuels, Public Transit |
CCS | Industry/Power | 1-4 | Geological Storage, Industrial Capture |
Land Use | Agriculture/Forestry | 3-6 | Afforestation, Soil Management, Diet |
India's Mitigation Efforts
National Solar Mission - 100 GW solar capacity target by 2022
Energy efficiency - PAT scheme for energy-intensive industries
Renewable targets - 175 GW renewable energy by 2022, 500 GW by 2030
Net-zero pledge - India committed to net-zero emissions by 2070 at COP26
Mitigation ≠ Adaptation - reducing emissions vs adjusting to climate impacts
CCS is mitigation - it prevents emissions from reaching atmosphere
Multiple strategies needed - no single technology can solve climate change
India's targets - 2030 renewable targets vs 2070 net-zero commitment