Modification of bentonite clay by a cationic surfactant to be used as a viscosity enhancer in vegetable-oil-based drilling fluid

Bentonite clays may be used as additives in drilling fluids aiming at viscosity correction. A surface modification procedure with the purpose of dispersing the clay in the organic phase of a vegetable-oil-based drilling fluid was performed. The fluids were prepared using soybean oil, lauryl alcohol triethoxylate, brine, bentonite modified by hexadecyl trimethylammonium bromide (CTABr), and barite. The clay modification step was performed using three different concentrations of cationic surfactant. To evaluate the surface modification of the clays, surface tension measurements and determination of contact angles on soybean oil with the capillary rise method were performed. A factorial design 23 with triplicate center point was conducted to evaluate the influence of the concentration of CTABr in clay modification, viscosity enhancer concentration in the composition of the drilling fluid and temperature on the rheological properties of the fluid: plastic viscosity, apparent viscosity, thixotropy and yield strength. As higher amounts of quaternary ammonium cations were adsorbed on clay surface, a decrease of the contact angle was observed, suggesting an increasing affinity for soybean oil. The study of the effect of independent variables showed that temperature is the most influential factor in the rheological properties of the prepared fluid. (C) 2016 Elsevier B.V. All rights reserved.