Laboratory Research on Offshore Oil-Based Drill Cuttings Cleaning

Drilled cuttings from wells drilled with oil based drilling fluids contain base oils and drilling fluid additives. These drilled cuttings, if discharged directly without proper disposal, will not only severely harm the environment, but also cause a huge waste of oils. To avoid this problem, the oily cuttings generated from offshore wells are generally cleaned with surfactant water solution. An oily cuttings cleaning fluid formulated with artificial seawater has this composition: 0.7% fatty alcohol polyoxyethylene ether AEO-5 + 0.3% anionic surfactant SDBS + 0.15% Na₅P₃O₁₀. In laboratory experiment, the oily cuttings were cleaned with this solution and the effects of drilling fluid additives and the minerals of the drilled cuttings on the residue oils on cuttings were investigated. It was found that the presence of drilling fluid additives in the residue oil on cuttings makes the cleaning more difficult. Compared with mica, feldspar and quartz, kaolinite cuttings are more difficult to clean. Based on laboratory experiments, the optimum cuttings cleaning technique was determined as follows: mixing speed = 500 r/min, ratio of solid to liquid = 1:4, cleaning time = 15 min, temperature for the cleaning = 25 ℃. After the cuttings were cleaned, the residue oils on cuttings can be reduced to less than 1%, which satisfies the requirements of the standard “Effluent Limitations for Pollutants from Offshore Petroleum Exploration and Production”.