Effects of interactions between solids and surfactants on the tribological properties of water-based drilling fluids

In oil well drilling the rotating pipe bears against the side of the hole at numerous points, giving rise to two main friction manifestations, known as torque and drag. Torque refers to the pipe resistance to rotation and drag to hoisting and lowering. Excessive torque and drag can cause unacceptable loss of power making oil well operations less efficient, especially in high-angle and extended-reach wells. In this work, it had been studied the effects of a surfactant additive (SA) and its dissolution in diesel (SB), on the tribological and rheological properties of water-based fluids (WBFs) formulated with two weighting materials (hematite and calcium carbonate). The tribological properties were established by measuring the coefficient of friction (CF) in conjunction with optical surface profilometry used to evaluate the wear behavior. The viscosity was determined as a function of shear rate in the interval 0.1–1000 s−1. Additionally, light scattering techniques were performed to study the dispersion stability of solid particles (weighting materials) in the aqueous surfactant solutions, and to correlate the solid–surfactant interactions observed with the tribological and rheological properties of WBFs. Based on the results, it was established that the evaluated surfactant additive can reduce significantly the CF independently of the weighting materials used, and that SA formulation has a superior performance in CF reduction than SB. Concerning the rheological properties, it was observed a viscosity increase in the polymeric WBFs formulated with hematite and SA, indicating strong interactions in the polymer–surfactant–solid system. In all other formulations there was no effect on the rheological behavior.