Evaluation of hydraulic controls for leakage intervention in carbon storage reservoirs

Abstract

Assuring the storage security of geologically sequestered CO₂ is essential for proper project management and long-term emissions reductions. Storage security relies not only on comprehensive site characterization prior to injection and careful reservoir management, but also on having a suite of intervention and remediation strategies available to implement if leakage occurs. In this study sequential stages of intervention are analyzed and evaluated. The first step in halting leakage is likely to be stopping CO₂ injection in the vicinity of the leak (also termed passive remediation). Results indicate that while passive remediation can reduce the leakage rate by an order of magnitude, completely stopping leakage may often require implementation of additional measures. Additional measures evaluated here focus largely on hydraulic controls, whereby water is injected or produced in or above the CO₂ injection reservoir in order to terminate leakage. The degree of residual trapping determines the extent to which leakage is ultimately reduced. For example, water injection into the overlying aquifer directly above a fault was able to completely terminate leakage for as long as water injection continues. Remediation was even more effective when water injection above the fault was combined with reservoir fluid production. We also show that in addition to hydraulic control methods, extracting 15–25% of the injected CO₂ can lead to permanent leakage termination. The role of reservoir heterogeneity on remediation efficacy was also examined and found to reduce the total amount of CO₂ leaked compared to a homogeneous reservoir. Overall this study demonstrates that temporally limited, multi-stage intervention strategies such as hydraulic barriers can permanently stop CO₂ leakage from storage reservoirs into overlying aquifers.