Impact of Surface Roughness on Rock Wettability

The wettability of the solid/fluid systems is an important property in several applications. The accurate determination of wettability in rock/fluid systems has a paramount role due to its fundamental influence on fluid distribution and the dynamics of multiphase flow in porous media. While various methodologies are available for the assessment of the wettability behavior of rocks, the goniometric approach, employed for contact angle measurements, is widely acknowledged for its direct applicability and appropriateness. This technique has the distinct advantage of facilitating wettability characterization for a broad spectrum of physicochemical conditions e.g., variations in pressure, temperature, and salinity. Several investigations have reported contact angles under diverse conditions for various rock/fluid systems. However, contact angles often depict an inconsistency in terms of the observed wetting behavior of specific rock/fluid systems under identical conditions. One prominent contributing factor to these discrepancies is rock's surface roughness. Typically, smooth and polished rock surfaces are utilized for contact angle measurements, and this study depicts that ignoring the inherent surface roughness of rocks can have notable impact on its wettability. This study analyzes the wetting characteristics of two distinct carbonate samples, each engineered to exhibit a spectrum of surface roughness values. Additionally, our investigation explores the impact of varying polish-abrasive sizes and types on both surface roughness and wettability, utilizing commercially accessible abrasives spanning a wide spectrum of dimensions, which include liquid silicon carbide (SiC) and sandpaper. The results contribute to an enhanced comprehension of the mechanisms governing wettability fluctuations at the millimeter scale and thus explain the underlying mechanisms influencing wetting properties.