Molecular-level elucidation of residual hydrocarbon effects on hydrogen adsorption and distribution in geological minerals

The presence of hydrogen within depleted geological formations is gaining significant interest due to its enormous capacity to hold hydrogen underground for storage and withdrawal. However, the adsorption and distribution of hydrogen in depleted geological pores concentrated with residual hydrocarbons remain unclear. To evaluate these physical characteristics under different geological minerals and varying thermodynamic conditions, we conducted a series of Grand Canonical Monte Carlo (GCMC) simulations. In this study, decane was introduced as a residual hydrocarbon component to represent long-chain heavy alkanes commonly found in depleted hydrocarbon formations. Furthermore, in our analysis, we considered minerals, including hydroxylated quartz, calcite, kaolinite, K-illite, and Na-montmorillonite, representative of common rock types found in geological formations, such as sandstones, shales, and carbonates, relevant to hydrogen geo-storage and production. Initially, we examined pure hydrogen adsorption on these minerals to understand the fundamental interactions. Decane was then incrementally introduced to the system, enabling a study of hydrogen interactions in the presence of residual hydrocarbons. To increase the system’s complexity, CO2 was introduced, allowing a detailed analysis of hydrogen distribution and interaction potentials within this multi-component environment. The findings revealed that hydrogen uptake showed negligible variation among the selected minerals in the absence of decane and CO2. However, incrementally introducing decane led to a linear reduction in hydrogen uptakes, ranging from 3% to 51%, depending on the mineral type. Additionally, the presence of ions caused significant shifts in the hydrogen surface adsorption peaks. The introduction of CO2 further decreased hydrogen uptake by 56 to 92% compared to the pure hydrogen uptakes by occupying the mineral surfaces, thereby reducing the availability of hydrogen near the surface. These results contribute to our understanding of hydrogen distribution in multi-component systems within depleted geological formations.