Influence of Surface Cleaning on the Wettability of Quartz/Oil/Brine Systems

Wettability is the measure of a liquid’s ability to adhere to or spread on a solid surface. The contact angle is a quantitative measure of wettability but can be affected by surface cleaning processes. The systematic investigation of wettability modification caused by surface cleaning is lacking. This study employs pure quartz substrates to examine the effect of rock surface cleaning on the wettability of rock/oil/brine systems. The nonporous substrates were polished and aged in solvents and formation fluids before being cleaned with different agents. Wettability was assessed using the contact angle technique at elevated pressures (0.1-50 MPa) and temperatures (353 K). The study also examined adsorption, surface morphology, roughness, and changes in rock strength using scanning electron microscopy (SEM), scanning probe microscopy (SPM), and nanoindentation. Fourier transform infrared spectroscopy (FTIR) and X-ray fluorescence (XRF) analyses were also performed before and after exposure to fluids. The results showed that interactions between quartz-brine, quartz-oil, and quartz-solvents significantly influence the wetting behavior. Our findings suggest that cleaning agents may not completely remove all adsorbed salts and crude oil components from the rock surfaces and may also adsorb onto the surfaces themselves, altering wettability. The presence of oxygen-containing groups, such as hydroxyl groups (O-H), increased the surface energy and promoted hydrophilic behavior, making the surface more water-wet. While the presence of nonpolar functional groups, like alkyl groups (−CH₃), aromatic C-H, and methylene (CH₂) groups, makes the surface more oil-wet. Interestingly, an increase in pressure has little or no effect on the contact angle of the n-decane/brine/rock system, but exposure to fluids did modify rock surface roughness and strength. Overall, this study provides valuable insights into rock surface cleaning and its influence on the wettability of rock/oil/brine systems. Understanding these interactions is crucial for various applications in the oil and gas industry.