Wellbore Integrity Impact on Carbon Leakage to Ensure Safe Geological Sequestration

AbstractSecure and safe geological sequestration is critical for the successful deployment of carbon capture and storage (CCS) projects and to mitigate global warming. Oil/gas reservoirs and saline aquifers, that are suitable for CO2 sequestration, often have older pre-existing wells near the potential CO2 injection wells. The legacy producing and abandoned wells have the potential to behave as CO2 leakage pathways, despite the existence of a good seal formation or structural certainty. In this study, this poorly understood and largely unknown leakage potential is researched to quantify the carbon leakage rate along one legacy well when carbon is injected into a storage formation in the Denver-Julesburg (DJ) Basin. This study investigates the risk of containment loss for a leaky well using a one-square-mile section of the DJ Basin. The results show that the completion of an older wellbore has a significant effect on the leakage rate results. A small portion (10-8) of the injected carbon can leak via a multi-segmented wellbore, while around 2.5% CO2 can leak to the drinking water layer via an open wellbore. Our results indicate that for secure carbon sequestration, a good geological storage site should be kept away from wells that have a surface casing depth of 476 ft or shallower and were drilled before 1994 in Colorado. The effective well permeability highly impacts the leakage rate, implying the importance of estimating the most representative value/range for this parameter. This risk assessment research is a part of the pre-feasibility study to support potential large-scale geological carbon storage operations in Colorado.