Pyrolysis of oil-based drill cuttings from shale gas field: Kinetic, thermodynamic, and product properties

Abstract

Oil-based drill cuttings (OBDC), as a by-product produced from the exploration and extraction of shale gas fields, have received increasing attention as both hazardousness and potential energy resources. In this study, the pyrolysis performance of OBDC was investigated using a thermogravimetric analyzer (TGA) and fixed-bed reactor. Results showed that the primary decomposition of OBDC occurred at 85–360 °C. The average activation energy calculated by model-free methods Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (OFW), Starink, and Friedman (FM) models were 53.11, 57.87, 53.38, and 64.23 kJ/mol, respectively. The reaction model depended on the degree of conversion. Moreover, high heating rates were conductive to predict the reaction mechanism. The analysis results of pyrolysis products showed that with the temperature increased from 450 °C to 600 °C, the oil yield presented a first increased and then decreased tendency, and reached the highest (14.94%) at 500 °C, then decreased to 12.10% at 600 °C. The oil was mainly composed of diesel fraction (C12-C22), which can be used as a fuel or raw material. Moreover, the lower heating value (LHV) of gaseous products was the highest (31.80 MJ/Nm3) at 600 °C. In addition, the oil content of char was far below 0.3%, and the heavy metal content in char was below the national standards (CJ/T 362–2011, China), suggesting that OBDC pyrolysis could achieve energy recovery and harmless treatment simultaneously. The results can provide a theoretical basis and data support for optimizing and developing OBDC pyrolysis reactors and processes.