Bonding Strength at the Cement-Casing Interface in Hydrogen Storage Wells

Given the growing interest in both short- and long-term underground hydrogen injection and reproduction, ensuring an impermeable sealing of the storage space for successful hydrogen containment is critical. Therefore, it is crucial to assess the capacity of borehole cement to maintain geomechanical integrity in the presence of changes in interfacial characteristics resulting from hydrogen exposure at the cement-casing interface. This study investigates how exposure to hydrogen affects the bonding strength and mechanical characteristics at the cement-casing interface in hydrogen storage wells typically remediated through squeeze cement jobs. New correlations link bond strength measured in double-direct shear (DDS) with x-ray micro-computed tomography (µ-CT) and ultrasonic velocity measurements. Compared to cement samples treated with nitrogen, the DDS tests showed a substantial reduction in shear bond strength for cement samples exposed to hydrogen, with a noticeable decrease in maximum shear strength and higher ductility. µ-CT imaging revealed that cement samples treated with hydrogen had increased bulk porosity with noticeable fractures, indicating weakened structural integrity of the bulk cement. These results were confirmed by ultrasonic velocity measurements, which revealed that samples treated with hydrogen had significantly lower P-wave velocities and Young's moduli. Such reductions in strength, indexed through reduced stiffness, highlight the risk of debonding and matrix cracking under repeated injection and production cycles. Importantly, both the cohesive strength at the cement-casing interface and the strength and stiffness of the cement decrease after exposure to hydrogen.