Study on the dispersion stability of kaolin in oil phase

With the large-scale development of shale gas, oil-based drilling fluids have found widespread application. However, a significant challenge arises in removing small harmful solids of oil-based drilling fluids after multiple uses. Investigating the stable mechanism of harmful solids in nonpolar solvents is crucial for their removal. Here, kaolin is chosen as the harmful solid phase. Various surfactants sodium bis(2-ethylhexyl) sulfosuccinate (AOT), sorbitan monooleate (Span 80), sorbitan trioleate (Span 85), cetyltrimethylammonium bromide (CTAB), oleic acid (OA), and stearic acid (SA) are used as dispersants to explore the dispersibility and stability mechanisms of kaolin in the oil phase. Results reveal that the Span 80 and Span 85 exhibit the best dispersibility and rheological performance for kaolin, followed by AOT, while SA shows the poorest dispersibility and rheological performance. Except for SA and CTAB, the other dispersants significantly improve the wettability of kaolin particles. X-ray diffraction (XRD) results indicate that all dispersants adsorb on the surface of kaolin. FT-IR and XPS confirm that nonionic surfactants Span 80 and Span 85 adsorb on the surface of kaolin through hydrogen bonding. Strong Zeta potential on the particle surface suggests that Span 80 and Span 85 stabilize the kaolin system through electrostatic repulsion mechanisms.