Ind. Eng. Chem. Res. 2005, 44, 6837-6844
6837
Treatment of Oil-Contaminated Drill Cuttings by Microwave Heating in a High-Power Single-Mode Cavity Hui Shang, Colin E. Snape, Sam W. Kingman, and John P. Robinson* School of Chemical, Environmental, and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, U.K.
This study demonstrates that oil-contaminated drill cuttings (OCDC) from North Sea platforms can be treated in a single-mode microwave cavity such that the residual oil levels can be reduced to below the current environmental discharge limits. A number of process parameters have been investigated, including microwave power, treatment time, sample mass, and moisture content. Although the discharge limits were not achieved in a number of cases, it is shown that enhancing the concentration of dielectric heaters or multistage processing are strategies which result in residual oil levels which are well below the environmental limit. For a sample mass of 100 g, it is shown that treatment times as low as 3 s can be sufficient to remove the required amount of oil; this is much faster than equivalent tests in multimode cavities. Introduction Background and Application. Oil-contaminated drill cuttings (OCDC) arise from drilling activities in the exploration and extraction of oil and natural gas, particularly in the North Sea oil fields. The drilling of wells requires the use of “drilling muds”, which act to lubricate the drill bit, provide hydraulic power, maintain the stability of the well-bore, and transport the drill cuttings back to the production platform.1 Three categories exist for drilling muds which define their base composition: water-based, oil-based, and synthetic. Stricter environmental legislation has resulted in increasing use of water-based muds (WBMs) in recent years, with oil-based muds (OBMs) used more sparingly where specific applications demand it. The drilling activities in the North Sea generally require oil-based muds because of their superior qualities in maintaining well-bore stability where the well passes through the poorly consolidated shales which are particularly prevalent in the East Shetland basin. OBMs are also regularly used in the drilling of deeper well sections and high angle wells, as their stability is maintained at the higher temperatures and more difficult conditions associated with these structures. The drill cuttings return to the production platform with the circulating drilling mud, where a primary separation is performed. The separated cuttings were, until recently, discharged straight into the sea without further treatment. Environmental legislation for the United Kingdom now stipulates that, in order to discharge cuttings into the North Sea, the residual oil levels must be
