A laboratory evaluation of superheated steam extraction process for decontamination of oil-based drill cuttings

Oil-based drill cuttings (OBDC), which originate from drilling operations in oil and gas fields, have been included in the 2016 National Hazardous Waste Inventory of China. In this investigation, the decontamination of two typical OBDC samples from shale gas fields, i.e., a diesel type from a vertical well (A) and a white oil type from a horizontal well (B), was conducted using superheated steam at near-saturation pressure. The effects of different pressures (0.6–5.5 MPa), temperatures (175–225 °C), and water flow rates (2–8 ml min−1) on the removal efficiency were studied in a semi-continuous laboratory apparatus. The results indicated that temperature was the most important parameter, followed by water flow rate and pressure. The OBDC characteristics also significantly affected the removal efficiency. Both the superheated steam and subcritical water present during treatment removed not only all extractable organics but also some other organics. With the optimal parameters of 2.3 MPa, 225 °C, and 6 ml min−1, 78.56% and 83.09% of total organic carbon were removed from A and B, respectively. After treatment, the OBDCs were not hazardous any more as their oil content has dropped to almost zero. Further analysis confirmed that this method possessed the advantages of solvent extraction (excellent solubility) and thermal desorption (high temperature). The results of X-ray diffraction and Sanning electron microscopy indicated that the microstructure and crystalline structure of in-organics in OBDC were not obviously changed during the treatment. As a result, this method can be considered as a new potential separation technique for treatment of OBDC.