Applied properties of oil-based drilling fluids with montmorillonites modified by cationic and anionic surfactants

Montmorillonites modified by cationic surfactants have been used in oil-based drilling fluids for a period of time, while few studies focused on the use of montmorillonites modified by both cationic and anionic surfactants in oil based drilling fluids. Compared with cationic surfactants, anionic surfactants have an advantage in thermal stability. Here, two parts of work were described. First, montmorillonites were modified by cationic and anionic surfactants through mechanochemistry. The structure and properties of organomontmorillonites were studied by X-ray diffraction, thermal analysis, contact angles and dispersion. Second, the applet properties including thixotropy, viscosity properties, gel properties and filtration loss resistance of oil-based drilling fluids with organomontmorillonites as additives were further studied at both room temperature (25 degrees C) and higher temperatures (200-220 degrees C). Characterizations indicated that cationic and anionic surfactants had intercalated into the interlayer spaces of montmorillonites, and the cationic-anionic organomontmorillonites had high surface polarity, better thermal stability and dispersion in high polar solvent than cationic organomontmorillonites. The properties of oil-based drilling fluids under both room and high temperatures showed that cationic and anionic organomontmorillonites performed better thixotropy, and had better rheological properties and less filtration loss than cationic organomontmorillonites in different oil-water ratio oil-based drilling fluids. The novel cationic and anionic organomontmorillonites have the potential to be widely applied in oil-based drilling fluids. (C) 2015 Elsevier B.V. All rights reserved.