Abstract
HypothesisActualization of the hydrogen (H2) economy and decarbonization goals can be achieved with feasible large-scale H2 geo-storage. Geological formations are heterogeneous, and their wetting characteristics play a crucial role in the presence of H2, 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 H2-wettability of caprock-representative minerals and their attendant structural trapping capacities. ExperimentGeological formations contain organic acids in minute concentrations, with the alkyl chain length ranging from C4 to C26. To fully understand the wetting characteristics of H2 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 C24, lauric acid C12, and hexanoic acid C6) for 7 days. To comprehend the wettability of the mica/H2/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). FindingsAt the highest investigated pressure (25 MPa) and the highest concentration of lignoceric acid (10−2 mol/L), the mica surface became completely H2 wet with advancing (θa= 106.2°) and receding (θr=97.3°) contact angles. The order of increasing θa and θr with increasing organic acid contaminations is as follows: lignoceric acid > lauric acid > hexanoic acid. The results suggest that H2 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 H2 containment security.
Highlights
Implementing a H2 economy entails H2 production via electrolysis and bi-reforming methane at an industrial scale followed by underground H2 storage (UHS), which can be retrieved at later stages for use [4,5,12,13,14,15,16,17,18,19,91]
The presence of organic molecules in geological formations is a pertinent factor, and the results reveal that organic acids have substantially altered the wettability in hydrophobic conditions in the presence of H2, regardless of the nature of organic acid [35]
The results suggest that a significant change in the H2wettability of mica is expected with an increasing carbon chain length of the alkyl group in the molecules of organic acids [42,43,44]
Summary
The world economies have been powered by fossil fuels, such as coal, natural gas, and oil, for more than 150 years [1,2]. The literature reports that organic acids are readily available in geo-storage formations because geological formations are anoxic where reductive conditions succeed [13,35,39,40,41,42,43,44,45]. Even though the presence of organics in geo-storage formations and caprock is quite minimal, their minute existence is sufficient to alter the initial hydrophilic condition of the storage medium into hydrophobic conditions (gas wet), which significantly influence the H2 trapping potential and containment safety [13,35,42,43,44]. The influence of organic acid contaminations on the sealing capacities of the caprock must be considered to accurately assess the rock/H2/brine wettability at realistic geo-storage conditions. The information from this research contributes to the broader-scale implementation of UHS and may assist in the curtailment of project uncertainty
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