Wettability of Kerogen in Shale Reservoirs by CO2/N2 Injection: Molecular Simulation of Temperature, Pressure, and Ion Effects

K Cheng and B Peng and M Arif and ZH Zhang and WF Lyu and W Jiang and XC Yang and HF Zhang, LANGMUIR, 41, 33788-33804 (2025).

DOI: 10.1021/acs.langmuir.5c03686

Understanding the wettability transition of shale organic matter in CO2/N2 environments is crucial for optimizing geological CO2 sequestration and gas recovery operations. In this study, molecular dynamics simulations were employed to investigate the wettability behavior of kerogen under CO2 and N2 atmospheres across a wide range of temperatures (298.15 to 378.15 K) and pressures (5 to 65 MPa). The effects of brine salt type, concentration, and gas mixture composition were also considered. Results show that increasing the CO2 pressure significantly increases the water contact angle on kerogen surfaces, indicating reduced water wettability. In contrast, N2 exhibits only a minor effect. Temperature has a weakening effect on contact angles under the CO2 environment but a negligible influence in the presence of N2. Salt cations such as Mg2+ and Ca2+ increase the contact angle more significantly than Na+ at the same concentration. Furthermore, as the N2 proportion increases in CO2-N2 mixtures, water contact angles decrease, revealing a stronger adsorption affinity of CO2 on shale organic matter. These findings provide molecular-level insights into how geological and compositional factors control the organic surface wettability of shales, contributing to the optimization of CO2 geological storage and enhanced gas recovery strategies.

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