Influence of organic molecules on wetting characteristics of mica/H 2 /brine systems: Implications for hydrogen structural trapping capacities.

Hypothesis: Actualization of the hydrogen (H ₂ ) economy and decarbonization goals can be achieved with feasible large-scale H ₂ geo-storage. Geological formations are heterogeneous, and their wetting characteristics play a crucial role in the presence of H ₂ , which controls the pore-scale distribution of the fluids and sealing capacities of caprocks. Organic acids are readily available in geo-storage formations in minute quantities, but they highly tend to increase the hydrophobicity of storage formations. However, there is a paucity of data on the effects of organic acid concentrations and types on the H ₂ -wettability of caprock-representative minerals and their attendant structural trapping capacities.
Experiment: Geological formations contain organic acids in minute concentrations, with the alkyl chain length ranging from C ₄ to C ₂₆ . To fully understand the wetting characteristics of H ₂ in a natural geological picture, we aged mica mineral surfaces as a representative of the caprock in varying concentrations of organic molecules (with varying numbers of carbon atoms, lignoceric acid C ₂₄ , lauric acid C ₁₂ , and hexanoic acid C ₆ ) for 7 days. To comprehend the wettability of the mica/H ₂ /brine system, we employed a contact-angle procedure similar to that in natural geo-storage environments (25, 15, and 0.1 MPa and 323 K).
Findings: At the highest investigated pressure (25 MPa) and the highest concentration of lignoceric acid (10 ^-2 mol/L), the mica surface became completely H ₂ wet with advancing (θ _a = 106.2°) and receding (θ _r =97.3°) contact angles. The order of increasing θ _a and θ _r with increasing organic acid contaminations is as follows: lignoceric acid > lauric acid > hexanoic acid. The results suggest that H ₂ gas leakage through the caprock is possible in the presence of organic acids at higher physio-thermal conditions. The influence of organic contamination inherent at realistic geo-storage conditions should be considered to avoid the overprediction of structural trapping capacities and H ₂ containment security.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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