Hydrogen underground storage potential in sandstone formation: A thorough study utilizing surface complexation modelling

This research focuses on the geochemical aspects of hydrogen underground storage, with particular emphasis on surface complexation modelling and its impact on surface potential and surface charge. The primary objective is to develop the first comprehensive surface complexation model specifically tailored for sandstone rocks, emphasizing key minerals such as quartz, kaolinite, and calcite, which are suitable for hydrogen underground storage applications. This model is intended to serve as a benchmark for more research in this field, providing a solid foundation for investigating and improving predictions related to wettability alteration. Additionally, the model has been integrated with hydrogen solubility to accurately capture changes in surface charge. The study identified six brine compositions with various minerals to examine the effect of monovalent and divalent ions. The results showed an increase in solubility with an overall reduction in salinity, and a decrease in divalent ions. The homogeneous surface complexation model demonstrated a neutral surface potential, attributed to an increased mole fraction of positively charged >SiOH⁺and a decreased in negatively charged >SiO-. Similar trends were observed in kaolinite and calcite minerals. The influence of pH was also explored, revealing a significant impact on the homogeneous quartz case, where an increase in pH shifted the surface potential from neutral to more negative. The heterogeneous cases exhibited less negative behavior as the quartz content increased per case, mainly due the increasing presence of positively charged species such as >SiOH⁺ and >AlOH⁺, and the reduction of the negatively charged >AlO^-. Increasing the salinity of the solution resulted in less negative surface potential, attributed to the abundance of positive divalent and monovalent ions boosted by increasing salinity, thus the formation of positive surface complexes.