The purpose of this research was to evaluate the refining of used lubricating oils (ULOs), and their possible use as drilling fluids. 17 treatments were evaluated and sulfuric acid and nonylphenol were used as reagents at concentrations of 0.12, 0.24 and 0.36 g/mL and temperatures of 40, 60, 80 and 100 °C. AT80 and AT100 ULOs treated at 80 and 100 °C without reagents, presented an average density of 0.84 g/cm-3, a viscosity of 76.3 and 75.3 cP, an electrical stability of 1,731.3 and 1,394.6 V and a flash point of 183 and 190 °C as higher. The ST40C1 and ST40C2 treatments, added with reagents, showed similar results to AT80 and AT100 in the evaluated variables, but they are more expensive treatments. According to the results, it is concluded that the refined ULO can be a substitute for the oil used in the formulation of oil-based drilling fluids.

The improper handling of used lubricating oil (ULO) in Tabasco, Mexico, and worldwide is a serious problem posing a high risk of soil and water pollution. Therefore, this study evaluated the handling of ULO in 10 municipalities in the state of Tabasco. Collection sites were chosen by simple random sampling. The ULO collected was assessed for solids, water, oil and density. The results show that small generators have the greatest potential to generate ULO in Tabasco. Huimanguillo, Comalcalco and Cardenas were the municipalities with the highest ULO generation. The ULO with the highest quality for its low water and solids content was collected in Jalpa de Mendez, Comalcalco and Car Dealerships. 1,287 automotive repair shops were tested in the 10 municipalities that were included