Effects of CO2 pressure on the dynamic wettability of the kerogen surface: Insights from a molecular perspective

Abstract

Wettability is crucial in controlling fluid flow in shale reservoirs, significantly impacting both enhanced oil and gas recovery and CO₂ geological storage. In this work, a high-pressure dynamic wettability mathematical model was established considering the roles of viscosity and adhesion to investigate the dynamic wettability of kerogen substrate at various CO₂ pressures. The wettability of kerogen substrate gradually transitioned from intermediate-wet to strongly CO₂-wet as CO₂ pressure increased. From a molecular viewpoint, the water-wetness of kerogen substrate was mainly affected by van der Waals and hydrogen bonds between O atoms in the kerogen substrate and the OH group in water molecules. As CO₂ pressure increased, a carbon dioxide film formed on the substrate due to competitive adsorption. The shielding effect of this film reduced both non-bond interactions and hydrogen bonds, resulting in lower water-wetness. From the viewpoint of activation free energy, CO₂ pressure primarily affected the water-wetness of kerogen substrate by modifying solid–liquid interactions, with little effect on viscosity. As CO₂ pressure increased, the activation free energy associated with adhesion increased, leading to a lower friction coefficient and a higher wettability activation energy. The link between the dynamic contact angle and the speed of contact line was first quantitatively characterized, and the dynamic wettability mechanism in the high-pressure CO₂-H₂O-kerogen system was clarified. The research provides new theoretical insights into fluid flow in nanopores and provides more reliable references for calculating the efficiency of enhanced oil and gas recovery and CO₂ geological storage.