Comparison of organo-sepiolite modified by different surfactants and their rheological behavior in oil-based drilling fluids

Sepiolite modified by surfactants has been used in adsorption, catalysts, etc. While few studies focus on organo-sepiolite (OSep) which is used in oil-based drilling fluid. In this paper, a kind of cationic-anionic organo-sepiolite (CA-OSep) was prepared to be applied in oil-based drilling fluids. The structure and properties of OSep were characterized by X-ray diffraction, FTIR spectrum, thermal analysis and surface contact angle (SCA) analysis. The effect of dosage and chain length of surfactants, and the ratio of cationic to anionic surfactants on OSep were discussed as well as the rheological properties of OSep/diesel system. Cationic surfactant of long chains had better adhesion to the surface of sepiolite than surfactants of short chains. Compared with cationic organo-sepiolite (C-OSep), CA-OSep has an advantage in thermal stability. The apparent viscosity, plastic viscosity and yield value of oil-based drilling fluids with OSep as additives were further studied at different temperatures. Results indicated that organic surfactants had been adsorbed on the surface of sepiolite, and the CA-OSep had higher surface polarity and better thermal stability in 5# diesel oil than C-OSep. CA-OSep presented a new kind of potential rheological control additive for oil-based drilling fluids, and would exhibit excellent thermal stability.