Abstract
Actualization of the hydrogen (H
) economy and decarbonization goals can be achieved with feasible large-scale H
geo-storage. Geological formations are heterogeneous, and their wetting characteristics play a crucial role in the presence of H
, 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
-wettability of caprock-representative minerals and their attendant structural trapping capacities.
Geological formations contain organic acids in minute concentrations, with the alkyl chain length ranging from C
to C
. To fully understand the wetting characteristics of H
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
, lauric acid C
, and hexanoic acid C
) for 7 days. To comprehend the wettability of the mica/H
/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).
At the highest investigated pressure (25 MPa) and the highest concentration of lignoceric acid (10
mol/L), the mica surface became completely H
wet with advancing (θ
= 106.2°) and receding (θ
=97.3°) contact angles. The order of increasing θ
and θ
with increasing organic acid contaminations is as follows: lignoceric acid > lauric acid > hexanoic acid. The results suggest that H
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
containment security.