Research Info

Wettability alteration analysis form gas-repellent to gas-wet with the aid of chemical agents has been subjected of numerous studies. However, fundamental understanding of the effect of surface tension of liquid on repellency strength, the change in the intermolecular forces due to the adsorption of nanoparticles onto the rock surfaces, and exposure of treated rock in brine are not well discussed in the available literature. In this study, X-ray diffraction, Atomic Force Microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied to characterize the treated and fresh samples. Dynamic and static contact angle measurements were then combined with six methods of surface free energy analysis; Neumann, Zisman plot, geometric, harmonic, acid-base, and Chibowski, to model liquid intermolecular forces effect on contact angle and to calculate the surface forces. Surface characterization results showed that adsorbed fluorine and silicon elements onto the calcite surface due to treatment in the nanofluid resulted in an increment of surface roughness. The weight percent of 0.93 and 1.22 and surface fraction of 0.265 and 0.014 for adsorbed Fluorine and Silicon were observed, respectively. A reduction for surface free energy in the range of 20–35 mN/m was observed for different applied approaches. The results of geometric, harmonic, and acid-base models indicated that calcite intrinsically has a mildly polar surface with a negative surface charge. It was revealed that the magnitude of the dispersive component was nearly 1.6 times greater than the polar component. For the treated surfaces, the geometric, harmonic, and acid-base methods showed a high reduction in the polar force of surface (<4 mN/m), which implied that the dispersive forces of the surfaces were dominant (~13 mN/m). The acid-base model estimated a negative surface charge for calcite and treated calcite. Also, a reversible reduction in water repellency due to exposure of treated sa