Study on pyrolysis law of shale gas oil-based drilling cuttings : kinetics and product characteristics

Abstract oil-based cuttings(OBDC)is a typical hazardous waste produced in the process of shale gas field development, and pyrolysis has been proved to be an effective treatment method, that can recover the harmful components and achieve resource reuse. In this paper, thermogravimetric experiments were carried out to study the pyrolysis kinetics, and the effects of pyrolysis temperature on the gas phase yield, oil quality and solid phase heavy metal migration were analyzed. The results show that the pyrolysis of OBDC is divided into three stages, and the light hydrocarbon cracking stage is the key control step of the pyrolysis process. In addition, the maximum weight loss rate of the sample with high heating rate appears at a higher temperature. Friedman (FM), Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink conversion methods can well fit the weight loss curve, and the estimated average activation energy is 185.5,184.16,166.17 and 176.03 kJ / mol, respectively. The estimated values are close and more accurate. The activation energy increases with the deepening of the reaction process. The solid phase products after pyrolysis accounted for more than 70% of the main products. The pyrolysis temperature had a great influence on the liquid phase yield, and the oil phase yield decreased by 1.17% from 450°C to 500°C. In the recovered mineral oil before and after pyrolysis: C15 ~ C28 pyrolysis C10 ~ C14 increased by 2.89%, C15 ~ C28 volatilization decreased by 3.26%, and high temperature aging increased C29 ~ C36 by 0.63%; aromatic hydrocarbons, as the coking parent, change from low ring to high ring. In addition, the content of heavy metals in the residue increased after pyrolysis, and more heavy metals were enriched in the residue. This study is helpful for the solidification of heavy metals and the recycling of solid waste, which is conducive to reducing energy and resource consumption and improving the processing technology of production.