Pyrolysis characteristics and kinetics of oil-based drilling cuttings in shale gas developing

In this paper, the thermal behavior of waste oil-based drilling cuttings (from shale gas fields in Chongqing) was examined at different heating rates ranging from 5 to 15 °C min−1 in inert atmosphere using a sync analyzer of thermogravimetry (TG) and differential scanning calorimetry (DSC). Four methods were used to analyze the distributions and variations of kinetics parameter (active energy (E) and frequency gene (A)): Coats-Redfern and other three iso-conversion rate methods (Flynn-Wall-Ozawa, Vyazovkin and Friedman). The experimental results indicated that the process consists of three steps, i.e., water evaporation, volatilization of light oil component and heavy oil cracking. TG curves moved toward higher temperature zone caused by thermal hysteresis with the increase of temperature rising rate. For volatilization of lightweight components, the E calculated by three iso-conversion rate methods changed a little with conversion, and had almost the same results as the CR method (14.39∼20.08 kJ·mol−1). For reactions of heavy oil cracking with mixed mechanism, corresponding E rose gradually with the increase of reaction time. The CR method shows nonlinear trends and the reaction models and kinetic parameters cannot be extracted from CR curves. The results by three iso-conversion methods showed that apparent activation energy was given as 155.74∼561.10 kJ·mol−1, 141.06∼524.96 kJ·mol−1 and 74.37∼605.10 kJ·mol−1, respectively.