Molecular insights into interfacial and flow dynamics of CH4-H2O mixtures in shale kerogen nanopores

F Lyu and ZF Ning and Y Kang and ZH Jin and ZJ Jia and WT Zhang and ZL Cheng, FUEL, 394, 135116 (2025).

DOI: 10.1016/j.fuel.2025.135116

Gas-water two-phase flow prevalent in shale organic matter nanopores is crucial for efficient gas utilization and enhanced gas recovery (EGR), and the role of interfacial behavior in nanoconfined space cannot be overlooked. In this work, we initially employed molecular dynamics (MD) simulations to investigate the CH4-H2O interfacial tension (IFT) and the wettability of H2O on the kerogen surface in the CH4 environment. On this basis, the coexistence and flow behaviors of CH4 and H2O in the kerogen nanopores were explored, and the effects of the interfacial properties and the underlying mechanisms therein were highlighted. The results indicate that the change of IFT induced by CH4 aggregation at the CH4-H2O interface and adsorption on the kerogen surface is the fundamental origin of the wettability transition. The stronger affinity of kerogen for CH4 leads to H2O as clusters in the nanopores, which gradually develops into an H2O bridge with increasing H2O saturation (Sw). The H2O clusters in kerogen nanopores pose a significant hindrance to CH4 flow. Moreover, the presence of H2O bridges restricts the CH4 flow, and they interact and constrain each other during the flow process, which is manifested by the morphological evolution in H2O bridge regulates the CH4-H2O flow. Kerogens with various maturities have different affinities for CH4 and H2O as well as heterogeneous surface morphologies of the kerogen matrix, which affect the occurrence of H2O bridges, resulting in differences in the flow states of CH4-H2O. This work shed light on the interfacial behavior and two-phase patterns of CH4 and H2O in the nanoconfined space of shale organic matter from a molecular perspective, furnishing new insights into energy and environmental issues.

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