Oil-based drilling cuttings pyrolysis residues at a typical shale gas drilling field in Chongqing: pollution characteristics and environmental risk assessment

With the rapid development of unconventional natural gas such as shale gas, many oil-based drilling cuttings and their pyrolysis residues are produced, which are defined as hazardous wastes. In this paper, the pollution status of petroleum hydrocarbons and the leaching toxicity of eight heavy metals (Pb, Cr, Zn, Mn, Cu, Cd, Ni, and Hg) in the pyrolysis residues were studied. The ecological risk and human health risk were evaluated in the scenario where pyrolytic residues were used for paving as building materials. The results showed that the content of petroleum hydrocarbons in the pyrolysis residues was 7643.16 ± 169.67 mg/kg. Zn in the pyrolysis residues was extremely polluted, Pb was moderately polluted, Cr, Cu, As were slightly polluted, and the leaching toxicity was far below the standard value. In the ecological risk assessment, the comprehensive potential ecological risk of multiple heavy metals in the pyrolysis residues was low. On the other hand, the pyrolysis residues had no non-carcinogenic risk to adults under the condition of paving, but there was an obvious non-carcinogenic risk to children, and the carcinogenic risk of adults and children was within an acceptable range. In addition, aiming at reducing the health risk of the population, suggestions were put forward to reduce the exposure risk of the population and the content of heavy metals in the pyrolysis residue, which provided a scientific reference for the standardized management of the pyrolysis residue of oil-based drilling cuttings and the research on the corresponding treatment process. Graphical abstract