Effect of salinity, mineralogy, and organic materials in hydrogen wetting and its implications for underground hydrogen storage (UHS)

Hydrogen is a green energy carrier, which appears to reshape the current energy supply chain. To develop a full-scale hydrogen supply chain, underground hydrogen storage has been proposed as a key method. However, one of the key hurdles in UHS is the fluid-rock interactions or hydrogen wetting. The interfacial reactions govern hydrogen wetting in underground reservoirs and thus determine the hydrogen flow and govern the amount of hydrogen trapping in porous media. Although the hydrogen wetting has been gaining attention, how the hydrogen wetting behaves in complicated underground circumstances remains in the shadow. To understand the nano-scale character of hydrogen wetting, a series of molecular dynamics (MD) simulations were performed to analyse the hydrogen distribution on kaolinite surface in function of salinity, mineralogy, and organic materials. We computed density distribution and the radial distribution function (RDF, g(r)) of each species. The results show that salinity can dramatically affect hydrogen distribution on the siloxane surface while negligible effects can be observed on aluminol (gibbsite) surfaces of kaolinite. Furthermore, the hydrogen distribution can be notably shaped by organic materials. Organic materials with acid functional group (–COOH) can generate a more hydrogen wetting surface than base functional group (–NH). This investigation reveals the governing mechanics of hydrogen-brine-kaolinite reactions at molecular scale, unravels the effects of hydrogen-brine-kaolinite reactions in hydrogen wetting and thus provides a paradigm to screen candidate sites for the UHS.