Study on Mechanisms of a Highly Adsorptive Polyol Ester Bonded Lubricant for Water Based Drilling Fluids

Common lubricants used in water based drilling fluids have weak adsorption on the friction interfaces of metals, and therefore are difficult to form dense and shear-resistant lubricating films thereon, which leads to high friction and torque during drilling. High friction and torque generally result in pipe sticking and high overpull or resistance during tripping of drill string. To improve the adsorption of drilling fluid lubricants on the surfaces of drilling tools, a polyol ester bonded lubricant was developed with a polyol and a long-chain fatty acid through dehydration condensation reaction. This new lubricant worked better in extreme pressure friction test, filter cake adhesion test and “point-to-point” friction test than similar products both from China and abroad. It can be used at temperatures up to 150 ℃. The working mechanisms of the lubricant were studied through four-ball friction test, SEM observation and X-ray photoelectron spectroscopy etc. It was concluded that the polyhydroxy structure of the lubricant can form bonded adsorption on the surface of Fe, which is stronger than the general physical adsorption, it thus can form a dense and shear-resistant lubricating film, having a thickness of about 45 nm, on the surfaces of drilling tools. The lubricant can also be adsorbed onto the surfaces of barite particles, thereby reducing the internal friction of a drilling fluid.