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How could depleted gas reservoirs be used for carbon capture and storage?

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natural gas The Troll A natural gas production platform in the North Sea, 80 km (50 miles) northwest of Bergen, Norway. Troll A, the largest movable structure ever built, rests on the seafloor some 300 metres (990 feet) below the surface and rises more than 100 metres (330 feet) above the sea. The platform regulates the recovery of gas from 40 wells located on the seafloor.

Depleted gas reservoirs are considered attractive sites for carbon capture and storage (CCS) because they are proven geological structures that have already demonstrated the ability to trap gases over long periods.12

To utilize these reservoirs for carbon sequestration, carbon dioxide captured from industrial sources or power plants is pressurized and injected deep underground into the porous sedimentary rock strata that previously held natural gas. Once injected, the CO₂ occupies the pore spaces within the rock. For this process to be effective and safe, the reservoir must be capped by an impervious layer of rock that acts as a seal, preventing the gas from leaking upward or laterally into the atmosphere.123

These sites are particularly valuable because they are "ready-made" storage areas, though their viability depends on rigorous leak-testing to ensure the absence of faults that could compromise containment. By isolating carbon emissions underground, this method serves as a critical strategy for mitigating the impact of greenhouse gases.132