CO₂ Storage: Closure and post-closure

The last phases – closure and post-closure – of storing CO₂ underground are very much a case of keeping an active and watchful eye as the variety of the CO₂ trapping mechanisms continue to develop and to become increasingly effective over time.

After CO₂ injection is stopped, the wells can be filled with cement and decommissioned. Once all the wells have been decommissioned, the site can be closed with the infrastructure gradually removed although MERV activities will remain active. After this has taken place, the post-closure phase begins. Limited MERV activities may continue for some time afterwards to ensure that no unwanted migration of the CO₂ takes place out of the storage formation and that abandoned and sealed injection wells are monitored and mended as needed if problems develop (under certain scenarios CO₂ can be corrosive to and degrade certain types of materials). In the long-run, rock sampling will be particularly useful to understand the long-term behaviour of CO₂ and the time taken for full residual, solubility and mineral trapping. All of which, will help further improve the planning and operation of future CO₂ storage sites.