The Post-Closure phase addresses post decommissioning—which has an extremely long time horizon of hundreds, if not thousands, of years. Post-closure requirements are determined based on site-specific risk assessments, taking into account risks identified during the original appraisal, the subsequent pre-closure site certification, and on modeled versus actual performance results during operation. A well-characterized site that has achieved its performance goals should require no long-term monitoring, while a poorly characterized site whose performance did not match modeled expectations will require long-term monitoring and possibly remediation. This phase includes the stages of monitoring, mitigation and confirmation.
During this phase, it will be necessary for the appropriate government authority or the entity in charge of post-closure ownership to continue monitoring, but only monitoring to detect leaks.
If a problem is detected while monitoring, then a remediation plan must be identified and implemented.
Once the mitigation plan has been implemented then the results must be monitored and measured to confirm that the mitigation has worked and that no further intervention is necessary.
A properly-engineered CO2 storage facility has a low risk of leakage. But if leaks do occur, they can be detected by two methods.
- By surface monitoring technologies, such as Tiltmeters provided by Halliburton's Pinnacle brand
- Through permanent and retrievable monitoring products provided through the Halliburton WellDynamics brand.
Once a leak is identified, its source can be accurately determined by wireline intervention using technologies such as the Halliburton RMT Elite™ reservoir monitor tool which detects CO2 flow behind casing.
After a leak source is determined, Halliburton's CO2-resistant reservoir conformance technologies can be employed to repair the leak and seal off problem zones in the reservoir. TheH2 Zero®service provides a polymer-based system recommended for sealing leaks in homogenous reservoirs. In more heterogeneous environments, the Halliburton BackStop℠ service, with its built in diverter technology, can be used to seek out and isolate low permeability zones, while allowing high permeability zones to be proportionally treated or remain untreated.
Leak repair confirmation
Once a leak has been treated, the effectiveness of the repair can be measured by using similar wireline intervention techniques as those used in leak identification. After confirming that leaks have been contained, the facility can reenter a post-closure monitoring phase.