Oil-Based Drilling Cuttings from Shale Gas Wells Treated with CO2 Switchable Hydrophilic Solvents: Priority Pollutant Migration and Produced Wastewater Assessment

Abstract

The exploitation of shale gas resources brings in abundant hazardous oil-based drilling cuttings (ODBCs). Herein, N, N-Dimethylcyclohexylamine (DMCHA) acted as the CO2 switchable hydrophilic solvents (SHSs), and the OBDCs treated with DMCHA were studied, especially priority pollutant migration and produced wastewater assessment during the extraction process. The petroleum hydrocarbon content of OBDCs decreased from 10.73 to 0.84 wt% after the DMCHA extraction was conducted at a DMCHA/OBDCs liquid–solid ratio of 20:1, 35 °C, and 200 rpm for 30 min. Using the CO2 switchability of SHSs, the petroleum hydrocarbon and DMCHA were recovered. There was wastewater, which was produced after recovering DMCHA, and the produced wastewater assessment showed that chemical oxygen demand, 5-day biochemical oxygen demand, total nitrogen, total organic carbon, and petroleum were 561.00, 238.00, 40.60, 309.00, and 0.27 mg/L, respectively. Meanwhile, phenols (0.0031 mg/L), naphthalene (0.0000129 mg/L), phenanthrene (0.000059 mg/L), anthracene (0.000058 mg/L), as well as heavy metal ions such as Cu (0.01 mg/L) could be detected in the produced wastewater. As a result, a priority pollutant migration mechanism from ODBCs to the produced wastewater was proposed. This would be helpful for the better management policy making of the ODBCs treated by using CO2 SHSs and the produced wastewater.