The Dispersion Stability of Bentonite in Water-in-oil Emulsions

Oil-based drilling fluids (OBDFs) are widely used in high temperature ultra-deep wells, high inclination wells, horizontal wells and various complex wellbores due to their excellent lubricity, high temperature stability, salt tolerance, and contamination resistance.However, the intrusion of drill cuttings during drilling destabilizes water-in-oil (W/O) emulsion drilling fluids.Therefore, bentonite, a common component of drill cuttings, was selected to study the factors influencing its dispersion stability in W/O emulsions.The macroscopic stability of the system was evaluated via static observation, and the dispersion state was characterized using optical microscopy.Additionally, the viscosity, contact angle of bentonite after adsorption of different surfactants, interfacial tension, and the charge of the bentonite particles were measured.Results indicate different surfactants affect dispersion stability through distinct mechanisms.The system stabilized by a nonionic surfactant exhibited low interfacial tension and the highest stability.Furthermore, dispersion stability increased with surfactant concentration.Finally, binary surfactant systems were formulated with Span80.Calcium stearate demonstrated a significant synergistic effect with Span80, enhancing the stability of bentonite dispersed in the emulsion, with an optimal ratio of 1:1.The mechanism of stable