Influence of different exchangeable cations (Li+, Na+ and Ca2+) on the modification effects and properties of organomontmorillonites used in oil-based drilling fluids/muds
Montmorillonite with different exchangeable cations (Li+, Na+ and Ca2+) in the inter spaces were modified using a combination of cationic and anionic surfactants, to prepare cationic–anionic organomontmorillonites (Li-organomontmorillonite, Na-organomontmorillonite and Ca-organomontmorillonite). The prepared organomontmorillonites were used in oil-based drilling fluids. Structure and properties of the cationic–anionic organomontmorillonites were studied using X-ray diffraction, thermogravimetry and contact angles. The properties of different oil–water ratios of oil-based drilling fluids/muds with added organomontmorillonite at room and high temperatures were studied using a rotary viscometer, filtration loss apparatus and a six-speed viscometer. The results showed that exchangeable cations in the inter-spaces of montmorillonite had an obvious impact on the structure and properties of the cationic–anionic organomontmorillonites. Of the three kinds of cationic–anionic organomontmorillonite, the cationic–anionic organomontmorillonite prepared from Li-montmorillonite had the largest basal spacing, best thermal stability and highest surface polarity which was followed by Na-montmorillonite and Ca-montmorillonite successively. Application of the research to oil-based drilling fluids/muds through adding different organomontmorillonites showed that Li-organomontmorillonite showed the best applied properties in full oil-based drilling fluids/muds at 180 °C. Na-organomontmorillonite showed the best applied properties in 80 : 20/90 : 10 oil–water ratio oil-based drilling fluids/muds at 180 °C. The oil-based drilling fluids/muds with added Ca-organomontmorillonite had the worst applied properties at 180 °C.