Carbon Capture and Storage: Sub-surface Storage

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Long term storage of carbon dioxide in the subsurface in the sub-surface is a viable approach to removing the greenhouse gas from our atmosphere and moving it to where a lot of the carbon came from, and where it has been stored geologically for millions of years.

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The sub-surface storage should be secure and with minimal leakage paths in order to keep any injected CO2 in place. This sub-surface container needs to have minimal leakage paths and have sufficient overall integrity to achieve its role of keeping the CO2 underground and in place.

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For this to be achieved the sub-surface evaluation needs to ensure  geomechanical integrity during the injection phase and over the long term storage lifetime. The main analyses to ensure this geomechanical integrity include:

- sub-surface geomechanical characterisation,

- cap rock integrity across the sub-surface formation, 

- fault seal integrity, and

- thermo-mechanical response to injection and equilibration.

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These analyses need to take into account the factors that will influence the long-term storage capability. Key considerations are:

- the geological history of the sub-surface,

- for depleted reservoirs, the production-depletion history and stress response,

- the horizontal stress variation across the sub-surface formation and caprice/overburden,

- the geological controls on the horizontal stress magnitudes (stress vs strain boundaries)

- the injection strategy,

- old production and new injection well locations, and 

- identification of potential leakage paths,

- long-term monitoring, surveillance and verification.