Pyrolysis kinetics and environmental risks of oil-based drill cuttings at China's largest shale gas exploitation site

Chongqing Fuling shale gas field, the largest shale gas exploration site in China, produces a large amount of oil -based drill cuttings (OBDC) every year, which is a hazardous waste. Traditional treatment methods such as solidification/stabilization did not recycle the valuable components such as petroleum hydrocarbons. Pyrolysis is proven to be an efficient method that can recover those components. This study firstly investigated the pyrolysis kinetics by two different methods on the basis of detailed material characterization, and then taking the workers and the surrounding ecological environment as the analysis object, the human health risk assessment (HHRA) and ecological risk assessment were evaluated respectively before and after pyrolysis. The results showed that the pyrolysis of OBDC was divided into three stages, and the cracking of light hydrocarbons stage was the key control step for pyrolysis process. The activation energy E increased gradually during the pyrolysis progress. The HHRA results showed that pyrolysis could greatly reduce the non-carcinogenic risk, carcinogenic risk and ecological risk by 59.6 %, 62.8 % and 75 % respectively. However, the carcinogenic risk after pyrolysis was still higher than the critical value 10-6.

Automated summary

Fuling shale gas field in Chongqing, the largest shale gas exploration site in China, generates a significant amount of hazardous waste called oil-based drill cuttings (OBDC) annually. Traditional treatment methods fail to recover valuable components such as petroleum hydrocarbons, while pyrolysis has proven to be an efficient method for their recovery. This study investigates the kinetics of pyrolysis using two different methods and evaluates the human health risk and ecological risk before and after pyrolysis. The results show that pyrolysis can significantly reduce non-carcinogenic risk, carcinogenic risk, and ecological risk, although the carcinogenic risk after pyrolysis still exceeds the critical value.