Test Methodology to Evaluate Cement Compatibility in Strategic Underground Gas Storage for Energy Transition

Abstract

Abstract The energy transition makes strategic Underground Gas Storage (UGS) a key technology to meet energy and emissions targets. Indeed, UGS can be useful not only for methane accumulation but also for other energy transition uses. No matter the type of storage utilized, the cement present in the well constitutes one of the main elements for the integrity of the entire process, as it must be able to ensure hydraulic insulation between the well and rock formation, especially in a reactive environment. This paper proposes experimental procedure to perform cement-fluid interaction studies. The cement to be used in the well must be compatible with the fluids to be stored i.e., carbon dioxide. Cement testing procedures related to standard placement and performance in the Oil & Gas (O&G) reservoir environment are detailed in the API Specification RP 10. Unfortunately, to date, there is no official standard procedures to verify the cement interactions with CO2 and other energy transition fluids. Although some results on the interaction between cement and reactive fluids are reported in the literature, these results cannot be easily compared with each other because the testing procedures are different, leading to specific constrain on the results. To better understand this problem, a deep analysis of the commonly used testing procedure phases was performed. The different steps of cement sample preparation process significantly affect the results of the chemical-physical characterization of the sample itself, particularly the curing and aging stages in the presence of a reactive environment. Starting from this point, a complete experimental procedure was designed to standardize the entire testing process even in the case of different reactive fluids. This method combines the typical approach of the solid/fluid interaction studies with the cement testing of the O&G industry reference standards, integrating petrophysical and compositional analyses. A particular focus is also provided on the experimental set-up and the precautions necessary to make the testing procedure more reliable and reproducible. On top of that, the instrumentation suggested, and the characteristic testing times reported in this article make this experimental procedure applicable to a large variety of reactive fluids. Consequently, this new standardized approach and the possibility to apply this method to different classes of fluids, makes it extremely versatile. Its usage constitutes a fundamental step to support specific cement formulation in UGS applications in the effort to ensure safe geological storage site utilization.