Grant: Alliance Grants

Carbon capture utilization and sequestration (CCUS) has been emerging as one of the most viable technologies to mitigate global carbon emission problem. Final stage of the CCUS process calls for the injection of CO2 into underground formations. Once it is stored into a geological formation, the necessity is that the CO2 stay there indefinitely, thus it will be permanently removed from the atmosphere. The wellbores that are used in CCUS projects to inject CO2 from surface to the selected storage reservoirs are sealed with steel casing and well cement. The purpose of the well cement is to support and protect the casing from corrosion and to act as a permanent barrier to flow of any fluid in the annular space between the casing and the wellbore wall. It is well known that there is a strong potential for CO2 to chemically alter conventional Portland based well cements and, hence, potentially compromise the lifetime integrity of CCUS wells. The ability to design well cements that will survive in CO2 environment is, therefore, a key to the successful application of the CCUS technology. Understanding mechanisms of cement microstructure alterations exposed to CO2-saturated formation water under downhole pressure and temperature conditions and how these impact fluid movement through cement body, and cement-casing and cement-rock interfaces is crucial for the assessment of cement performance in CCUS wells. Comprehensive experimental and numerical studies of the mechanisms of cement microstructure alteration under the influence of CO2-saturated formation water and how these changes impact the risk of fluid movement through the cement microstructure and at cement-casing-rock interfaces are, therefore, proposed. Improved understanding of the drivers behind fluid leakage (i.e. chemical alterations of the cement microstructure upon exposure to CO2-saturated formation water, resulting formation of micro-channels along the interfaces) by direct imaging and subsequent modeling of the cement pore structure and cement/casing/ formation interfaces, as proposed in this project, will allow for the design and development of new, reliable barrier technologies that can be used for cost-effective mitigation of fugitive CO2 emissions from CCUS wells.