Enhancing Well Integrity in CCUS Applications: The Role of Insulating Gas Blankets

Abstract As part of the Net Zero emission plan, capturing CO2 and storing it in geological formations is a key strategy. Existing wells are being repurposed, and new wells drilled to inject CO2 into depleted reservoirs as well as saline aquifers. These operations are expected to continue for decades, making long-term well integrity critical. The variability of the CO2 phase and the rapid and severe temperature drop during vaporisation challenge well integrity, impacting tubulars, connections, annular fluids, cement sheaths and casing shoes. Integrity of outermost strings and associated cement sheaths and supporting formations is a key concern with particular focus on compressive loads. This study examines the use of insulating gas blankets in the tubing-to-casing annulus and outer annuli as a thermal barrier, mitigating the cooling effects of CO2 while addressing the potential issues related to fluid shrinkage and pressure stability maintenance. Gas blankets in wellbore annuli are investigated using a fit-for-purpose application that integrates nodal flow assurance for wellbore temperature and pressure predictions with tubular stress analysis of casing and tubing strings. Gas blanket effectiveness is driven by the relatively low conductivity of gases and negation of natural convection of annular fluids. Surface chokes and reservoir injectivity are incorporated into the flow assurance and stress analysis within a nodal framework. CO2 injection is simulated with particular emphasis on especially cold events, such as injection re-start, turn-down and steady low-rate injection. Annular fluid contraction and expansion are accounted for as loading conditions on tubulars. By combining these factors, an operability envelope for the tubing-to-casing annulus (A-annulus) is established, ensuring pressure remains within limits to maintain integrity. A case study is presented to illustrate the design of a well incorporating nitrogen gas blankets within its design framework. Preliminary results indicate that insulating gas in the annuli effectively reduces heat transfer, thereby maintaining well integrity during CO2 injection. Additionally, it provides a buffer against annular fluid contraction, enhancing long-term well safety and performance. The required gas volumes are determined by predicted temperatures from flow simulations and tubular loads. Such analysis is crucial for newly drilled CO2 injection wells and for repurposing existing wells, ensuring reusability. Thermally induced compression loads on outer and structural strings near surface require careful review, including specification and qualification of connections. Applying insulating gas blankets in CO2 storage wells is a novel approach. While gas blankets are commonly used in deep-water wells, their application in platform and land wells is rare, making this approach unconventional in such settings. Furthermore, gas blankets have yet to be deployed widely in CCUS wells, presenting a unique opportunity for innovation. This method offers an effective and cost-efficient solution for managing low-temperature effects and enhancing well integrity in CCUS applications.