Carbon Sequestration Sites

Coal seams, oil and gas reservoirs, saline formations

• Coal seams: abandoned, uneconomic seams can store injected CO2. Coal surfaces naturally adsorb the gas.
• Depleted oil and gas reservoirs: strong candidates. Their rock trapped hydrocarbons for millions of years.
• Deep saline formations: porous rock filled with salty water. They offer the largest total capacity.
• All three are genuine sites. None is a distractor.

Capture, storage and sequestration

• Capture: separate CO2 from a plant’s exhaust or from air.
• Storage: keep that CO2 in a chosen place, such as deep rock.
• Sequestration: move carbon into a store and keep it for a meaningful time.
• CCS joins capture, transport and geological storage.
• CCUS also includes uses for captured CO2.
• Storing fossil CO2 from a cement plant prevents a release. It is not automatically removal of CO2 already in the air.
• Forests and soils are natural sinks, not injection sites.
• Sources: IEA CCUS overview and IPCC land chapter.

Natural sinks versus engineered stores

• These pathways have different timescales.
• Geological storage needs evidence that injected CO2 stays contained.
• Source: IPCC carbon-cycle assessment.

Supercritical injection, and a sealing cap rock

• CO2 is compressed into a dense, liquid-like supercritical state before injection.
• A safe site needs a porous reservoir rock to hold the CO2.
• It also needs an impermeable cap rock on top to stop the gas rising.

One cement plant to the rock

• This is a teaching example, not a named Indian plant.

1. Capture. Equipment separates some CO2 from the exhaust. The plant still measures what it releases.
2. Prepare. The CO2 is dried and compressed.
3. Transport. A pipeline or other system takes it to the site.
4. Choose a site. Scientists study porous rock, the seal, faults, old wells and nearby water.
5. Inject. A well sends CO2 deep. Operators control pressure and track the plume.
6. Monitor. Tests check the well and underground movement. Checks continue after injection stops.

• Count capture energy, transport, leakage and remaining plant emissions.
• Capture alone does not prove a net climate benefit.
• Sources: IEA on how CCUS works and IPCC on geological storage.

Saline formations dominate capacity

• Deep saline aquifers underlie huge areas.
• Most commercial-scale storage is expected there, not in coal seams.
• A saline aquifer holds salty water, not drinking water.

What makes each site different?

• Deep saline aquifer: large potential. The seal, pressure and water movement need study.
• Depleted oil or gas field: existing records help. Old wells may be leakage paths.
• Unmineable coal seam: CO2 sticks to coal surfaces. Capacity depends on the seam.
• Basalt: CO2 may react with minerals and become solid carbonate. It needs the right rock and water.
• Dissolving in salty water and forming minerals add other traps over time.
• Sources: IPCC geological storage and US NETL storage FAQ.
• Compare basalt, ocean alkalinity and mine injection.

Part of CCS, and not yet at scale

• These sites are the storage step of Carbon Capture and Storage.
• CCS aims to cut emissions from coal and gas plants.
• Few commercial CO2 projects in coal beds exist today.
• Coal seams hold less capacity than oil, gas or saline sites.

When is a climate claim credible?

• Permanence: will the carbon stay stored for the claimed time?
• Additionality: would the storage have happened anyway?
• Leakage: does carbon escape, or does the project push emissions elsewhere?
• MRV: measure, report and let others verify.
• Forest carbon can be lost through fire or clearing. Soil gains may slow, called saturation.
• Underground projects must watch pressure, wells and the CO2 plume.
• Energy used for capture also changes the net result.
• Sources: IPCC land report and IPCC geological storage.

India: potential is not proven storage

• India’s Department of Science and Technology (DST) reported a 2022–23 study of possible stores.
• It looked at saline aquifers, basalt, coal beds and oil-recovery routes.
• It described a planned pilot linked to the Gandhar field in Gujarat. A planned pilot is not proof of commercial storage.
• DST launched a CCUS research roadmap in December 2025, including cement and steel.
• India also has natural stores in forests, soils and coastal wetlands.
• Sources: DST annual report 2022–23 and DST roadmap announcement.

Exam traps

• Capture is the separation step. Storage is the place that keeps CO2.
• Fossil-source CCS avoids emissions. It does not remove old CO2 from air.
• A saline aquifer is not an underground lake of usable water.
• Any site needs testing. A rock type alone proves little.
• Carbon use is not always long-term storage.
• See also stratospheric aerosol injection in the wider climate toolkit.