Study on Pyrolysis Kinetics, Behavior, and Mechanism of Organic-Rich Tuffaceous Mudstones Based on Thermogravimetric Analysis

Abstract

Organic-rich tuffaceous mudstones are important oil and gas resources. The systematic study of the pyrolysis kinetics and characteristics can not only provide the theoretical basis for the rational development and efficient utilization of these rocks but also is an important complement to the theoretical research on the pyrolysis kinetics of organic-rich rocks. In this study, the pyrolysis kinetics, behavior, and mechanism of the organic-rich tuffaceous mudstone in the Junggar Basin were clarified by thermogravimetric analysis. The organic structure and mineral composition were identified by Rock-Eval, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The results indicated that the mudstone could be described as a type II kerogen with good hydrocarbon generation potential. The mudstone included up to 80.7% quartz, which is associated with Carboniferous volcanic activity. Four isoconversional methods were used to evaluate the activation energies. A novel and simplified method was proposed to separate the pyrolysis processes using the Coats−Redfern method based on the differences in reaction models and activation energies. The pyrolysis processes were divided into four stages, and the reaction models of each stage were preliminarily clarified. The reaction models were further modified by the accommodation function The results showed the kinetic parameters, and the reaction models of each stage were significantly different. Moreover, the obtained kinetic parameters and optimal reaction models can well characterize the pyrolysis processes and mechanism of the tuffaceous mudstone. The results of thermogravimetric-FTIR (TG-FTIR) indicated that the main pyrolysis hydrocarbon volatiles were methane, C 2+ aliphatic hydrocarbons, and aromatics. And the types and yields of pyrolysis volatiles differed at each stage.