Uncertainty Quantification and Monitoring of CO2 Storage in Depleted Gas Fields with Legacy well Leakage Risk

The EU Directive on CO2 storage stipulates that site-specific storage permits should include a monitoring plan and require repeated comparison of monitoring data against expected behaviour. Monitoring data should provide sufficient information about the state of risks that are identified in the storage license. We present an application of two quantitative approaches that could guide operators and regulators in evaluating monitoring plans for storage in depleted gas fields. Our application case is a synthetic gas field that contains 2 potentially leaking legacy wells. A large ensemble of model realizations is first history matched to production data and then used to simulate CO2 injection and BHP data gathering for scenarios with and without leaks. Application of both forward and inverse uncertainty quantification methods suggest that injection BHP data alone may not be sufficient to distinguish the effects of significant leaks from those associated with geological uncertainty.