Effects of Hydrogenated and De-Hydrogenated Organic Hydrogen Carriers on Carbonate Wettability for Hydrogen Geological Storage

Organic hydrogen carriers (OHCs) have emerged as a promising solution for the efficient large-scale storage and transport of hydrogen, thus helping to address the increasing demands for renewable energy and decarbonization. The ability to store hydrogen geologically is influenced by the wetting properties and interfacial forces between the OHCs and subsurface formations, with significant impacts on the residual saturation, fluid flow dynamics, injection/withdrawal rates, and containment reliability. Herein, the advancing and receding contact angles and interfacial tension (IFT) of methylcyclohexane (MCH) and toluene are measured on calcite substrates in the presence of 1 M NaCl solution under natural physio-thermal geological conditions (298-343 K, 1-20 MPa). In addition, the MHC-exposed calcite samples are characterized via atomic force microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, and total organic content analysis. The results suggest that the wettability and IFT values increase with increasing pressure and decrease with increasing temperature. This is attributed to increased intermolecular interactions between the liquid molecules and solid surface, along with the reduced density and surface energy of each liquid on the positively charged rock surface. However, due to the density difference between hydrogenated and dehydrogenated forms, MCH has a higher IFT and lower wettability than toluene at a given pressure and temperature. The findings demonstrate the viability of OHC integration into carbonate reservoirs for enhanced and secure hydrogen storage capability, and underscore the importance of optimizing OHC interactions with geological substrates to improve the hydrogen storage efficiency for advanced sustainable energy solutions.