On hydrogen-cement reaction: Investigation on well integrity during underground hydrogen storage

Abstract

Underground hydrogen storage (UHS) is becoming a promising technology to help achieve full hydrogen economy and support the energy transition to carbon net-zero. One of the important parameters for securing UHS for example in depleted gas reservoirs is related to the wellbore integrity and cement seal, which is rarely addressed. When hydrogen is injected, it can react with the cement around the wellbore, and cause various alterations in cement petro-physical properties. Therefore, it is crucial to understand the associated reactions between hydrogen and cement and their implications for cement degradation. In this study, hydrogen injection experiments were performed on two cement core plugs (class G) under 1400 psi and 75 °C for 125 days, and the impact on cement integrity was evaluated. The results show low reactivity of hydrogen with cement and minor alteration in the petro-physical properties of the cement samples. The XRD results show a minor increase in Alite contents after hydrogen injection, while the observed calcite growth was attributed to the cement hydration process. Despite the presence of high mobility elements such as Ca, Mg, K and Al in the cement plugs, the minor redox reactions between cement minerals and hydrogen inhibit the precipitation of high-density minerals. However, we indeed observed for the first time an increase in cement weight and density with hydrogen injection, which suggest that hydrogen/brine injection may promote the precipitation of high density products. This caused a reduction in the CT porosity by 8.86% and 8.43% in samples C#1 and C#2 respectively. However, the total reduction in porosity is considered minor, suggesting a limited impact on cement integrity -which is favorable for UHS-. Furthermore, the alteration in the statistical distributions of P- and S-waves caused a minor increase in Poisson's ratio and dynamic elastic modulus (E), suggesting a low risk of wellbore cement degradation during UHS. The obtained results provide clear analyses of the reactivity of cement to hydrogen injection, and suggest that no significant impact on wellbore integrity or cement seal would be expected during UHS.