Formulation effects on the lubricity of o/w emulsions used as oil well working fluids

In oil well drilling, completion, and maintenance operations, 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 these cases, lubricity becomes one of the main functions of the fluid. In the oil industry, there are oil well working fluids of different nature, classified according to the external phase as water-based fluids (WBFs), oil-based fluids, and pneumatic or gas-based fluid systems. Within WBFs, there are oil-in-water (O/W) emulsions, developed as a technological solution for oil well operations in low-pressure reservoirs. In this work, tribological properties of O/W emulsions have been studied as a function of their physicochemical formulation, especially oil type (nonaromatic mineral oil [NAM-oil], diesel) and surfactant concentration (1, 2% w/v) along with the oil/water ratio (70/30, 50/50) as formulation variables. The lubrication performance was established by measuring the coefficient of friction (CF), and optical microscopy imaging in conjunction with optical surface profilometry was used to evaluate antiwear properties. Additionally, contact angle measurements were performed to correlate the wettability phenomenon with the lubricity of O/W emulsions. Based on the results, it was established that with the surfactants mixture used in this study, the oil type does not have a significant effect on the CF of O/W emulsions, due to the similar wettability behavior observed at the metal surface. However, NAM-oil/W emulsions have better antiwear properties than the diesel/W emulsions. Also, the lubricity performance and antiwear properties of O/W emulsions are affected by oil/water ratio and surfactants mixture concentration, showing a systemic interaction between these two parameters.