Influence of Rock Surface Roughness on the Contact Angle in the CO₂ Geological Sequestration Process

In this study, the influence of sandstone surface roughness on the solid–liquid contact angle in the CO2–fluid–rock system was quantitatively characterized, an aspect that is often overlooked or is only verbally mentioned in the literature. First, five Berea sandstone samples were polished to different levels of surface roughness. Three-dimensional optical scanning technology was used to establish surface models for the different samples, and their roughness values were calculated. Subsequently, the solid–liquid contact angles of all samples in the CO2–fluid–rock system were measured under various temperature and pressure conditions. The analysis of the experimental results showed that surface roughness has a significant impact on the solid–liquid contact angle, showing that the greater the roughness, the smaller the contact angle. At room temperature and pressure, an increase in roughness by one level results in a 25–35% decrease in the solid–liquid contact angle. However, under in situ reservoir conditions, this magnitude of change is reduced to approximately 20%. Based on experimental data, the contact angle estimation formula for rocks with different roughnesses has been regressed, and it has been verified to have high accuracy, revealing the relationship between the solid–liquid contact angle and surface roughness in the CO2–fluid–rock system.