chapter  9
Formation of Tribofilms from Surfactants with Different Degrees of Ethoxylation on Steel Surfaces in the Boundary Lubrication Regime
Pages 37

Drilling fluids used in the oil industry are complex mixtures of a base component and different additives. Each additive provides a specific property, which helps to control the performance of the fluid and permits an efficient drilling operation. The lubricity function of a drilling fluid is extremely important due to the existence of large frictional forces at all stages of well construction (drilling, completion, and maintenance). The sources of frictional forces include pipe resistance to rotation and raising and lowering movements of the drill bit and string inside the well in contact with the wellbore (metal to rock) and the casing (metal to metal). The improvement of the fluid lubricity can be achieved using lubricant additives, generally available as film-producing liquids, solid beads, powders, and fibers. Investigations were conducted to establish the structures of surfactants that can be added to drilling fluids to enhance their ability to reduce friction and wear in drilling apparatus. The adsorption effect of surfactant mixtures with different degrees of ethoxylation on the tribological properties of bilayers (tribofilms) formed on steel surfaces under boundary lubrication conditions was evaluated. Three surfactant mixtures containing 20% w/w ethoxylated (4, 7, or 9 EO) lauryl phosphate ester and 80% w/w ethoxylated (4, 7, or 9 EO) lauryl alcohol were used. The stability of the tribofilms formed on steel surfaces and the wear behavior of surfactant mixtures in aqueous solutions at 1% w/w concentration at pH 4, 7, and 10 and at three different temperatures (25°C, 49°C, and 80°C) were evaluated using dynamic friction tests at constant velocity and strain oscillation. The wear behavior was determined by analyzing the wear with an optical surface profilometer. The effect of surfactant composition and pH and temperatures on friction and wear are discussed.