Effect of High-Temperature CO2 on the Surface Characteristics and Wettability of Anthracite

SQ Ma and BQ Lin and JJ Zhao and Q Liu and XL Zhang and T Liu, ENERGY & FUELS, 39, 14545-14561 (2025).

DOI: 10.1021/acs.energyfuels.5c02828

Wettability plays a crucial role in the efficient extraction of coalbed methane (CBM). The injection of high-temperature CO2 from hot flue gas into coal seams can alter the morphology and functional group content on the coal surface, considerably affecting the wettability of water there. In this study, experiments were performed to explore the changes in oxygen-containing hydrophilic functional groups and the pore-fracture network characteristics on the coal surface after high-pressure CO2 treatment at different temperatures and analyze how these changes influence the coal surface wettability. Furthermore, molecular dynamics simulations were conducted to construct coal surfaces with varying roughness levels and examine the wetting behaviors of droplets with different water molecule contents and occurrence forms on these surfaces. The following findings were yielded based on the experimental and simulation results: For the anthracite used in this study, the content of oxygen-containing hydrophilic functional groups is minimal and changes slightly with the rise of CO2 temperature. As a result, their impact on coal surface wettability is negligible. In contrast, the complex morphological changes exert a more significant effect. Water adsorbed on the coal surface in the form of droplets or films exhibits different wetting behaviors depending on surface roughness. When the droplet comprises a small number of water molecules, smoother coal surfaces achieve better wettability. However, larger droplets find it easier to wet rougher coal surfaces. The sharp peaks on rough coal surfaces hinder the formation of water films, whereas the even distribution of water molecules across different regions of smooth coal surfaces conduces to the stable existence of water films. The research findings can provide theoretical support for the postinjection wettability regulation of coal seams.

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