Impact of Cement Additives on Capillary Pressure and Petrophysical Properties in Oil Well Cementation for Geological Hydrogen Storage

Cement integrity is crucial for ensuring wellbore stability, particularly in applications relevant to hydrogen storage. A few studies have focused on studying the geochemical reactions between cement and hydrogen, overlooking the impact of petrophysical properties and capillary effects, which are vital for understanding fluid migration and maintaining sealing integrity. Motivated by this gap in knowledge, we present an experimental study on the impact of various cement additives on the petrophysical properties and capillary pressure of oil well cement under hydrogen storage conditions, an area that has not been adequately studied before. Scanning electron microscopy (SEM) analysis reveals that all cement samples exhibit a relative distribution of fine capillary pores and interconnected voids, predominantly composed of oxygen and calcium. Some microcracks are observed upon the addition of cement additives, potentially due to shrinkage or thermal stresses. However, incorporating nanosilica has a minimal effect on the cement crystal structures and fracture development. The results from NMR tests indicate slight porosity variations (6.75% to 8.5%) with negligible effects from high total organic content (TOC) in additives, maintaining high capillary pressure. The presence of microcracks does not significantly alter gas permeability, as the average permeability decreases from approximately 0.8 to about 0.15 mD with the addition of cement additives, while nanosilica does not result in substantial changes in permeability values. Capillary pressure measurements showed strong hydrophilic behavior in all samples, with minimal water displacement (less than 0.03% at 150 psi), indicating a high capillary pressure. Neither cement additives nor nanosilica significantly affected wetting behavior or water displacement, affirming the cement samples’ inherent hydrophilicity and capillary pressure despite their inclusion. These findings confirm that the cement maintains stable petrophysical properties and capillary behavior with additives, which is essential for effective underground hydrogen storage (UHS) and contributes to evaluating cement seal integrity to prevent potential leaks.