Improving Wellbore Seal Integrity in CO2 Injection Wells

Abstract

Abstract The challenges associated with the construction of an injection well for carbon sequestration are cross disciplinary, but highly manageable. Site selection, reservoir identification and formation evaluation involve geological and reservoir specialists that perform detailed evaluations of the subterranean environment.[1–4] Materials selection identifies components that are designed to withstand the unique chemical and physical environments of these wells. Sealant selection is key to providing long term integrity of any well, with Portland cement being the material of choice for most oil field applications. Work on Carbon Sequestration in subterranean formations has renewed interest in investigating the long term effects of CO2 on Portland cements. Portland cement will react with the injected CO2, and while recent research indicates these conventional cements are not a concern, additional work is ongoing to improve the long term effectiveness of the wellbore sealant. Efforts have focused on enhancing the properties of Portland cement by reducing the permeability of the set cement, lowering the concentration of materials in the cement that react with CO2, or replacing the conventional Portland with specialty cements. Complementing technologies that have been used to further promote long term seals include the use of in-situ swell packers, and self healing cements. Additional work has been done in evaluation of the long term stress environment of the well. This work goes beyond the simple drilling and completion of the well to include input from long range reservoir and wellbore stress modeling through the full life cycle of the well. These stresses are evaluated to confirm the selected sealants can withstand the changing stress environment. This paper discusses various identified solutions to the challenges of selecting a proper wellbore sealant for a CO2 injection well. Additionally, the paper reviews the available sealant technologies, their application, and includes a discussion of stress modeling for these wells. Background Successful carbon capture and sequestration (CSS) depends on a identifying a place to permanently store the captured CO2. Geological formations are currently considered the most promising sequestration sites, with three types being considered the most promising: depleted oil and gas reservoirs, unmineable coal seams and deep saline formations. To sequester CO2 into any of these formations requires careful site selection and the proper installation of injection wells. Many of the depleted oil and gas reservoir sites have existing wells, which creates an additional challenge of properly sealing those potential leak paths.