A Comprehensive Study on the Impacts of CO2 and H2 Storage on Well Cement Integrity

Abstract The interactions between hydrogen and carbon dioxide (CO2) with wellbore cement are not fully understood, raising concerns about cement degradation during carbon capture and storage (CCS) and underground hydrogen storage (UHS). This study examines the geochemical, petrophysical, and geomechanical properties of cement before and after exposure to hydrogen and CO2. Cement samples were saturated in brine of 30000 ppm and exposed to the gases at 500 psi and 50°C for 30 days. Hydrogen exposure led to a 50% increase in brownmillerite, a 70% decrease in ettringite, and a reduction in porosity and permeability by 2% and 40%. Compressive strength and Young's modulus increased by 35% and 6%. CO2 exposure caused the formation of calcite (8.7% of the composition) and complete alite depletion, reducing porosity and permeability by 98% and 87%. Compressive strength and Young's modulus rose by 126% and 161%. This study is the first to comprehensively compare cement properties before and after hydrogen and CO2 exposure under the same conditions. The findings suggest hydrogen and CO2 do not weaken cement strength and can even heal fractures, reducing fluid losses.