Thermogravimetric Pyrolysis Behavior and Kinetic Study of Two Different Organic-Rich Mudstones via Multiple Kinetic Methods

Two representative organic-rich mudstones from the Middle Permian (MP) and the Upper Carboniferous (UC) around the Fukang Depression in the Junggar Basin were selected to study and compare the pyrolysis behavior and kinetics. The MP and UC were described as type I and type II kerogen, respectively. The FTIR and XRD results revealed that the MP contains carbonates and different clay minerals compared to the UC. Peak deconvolution was used for the UC to delineate the pyrolysis process to better understand and compare the similarities and differences in the pyrolysis kinetics of the two mudstones. In addition, the Coats-Redfern method was employed to further differentiate the reaction stages based on the differences in the reaction models during pyrolysis. The kinetic results revealed that the activation energy, pre-exponential factors, and reaction models of the two mudstones have some similarities and differences. Combined with the analysis of the pyrolysis volatiles, the UC sample can release more CH4, CO, CO2, and aromatic hydrocarbon compounds at high temperatures, indicating that the UC has more oxygen-containing functional groups and aromatics, while the MP has more aliphatics. Through the above studies, the pyrolysis kinetics and mechanism of two organic-rich rocks could be clarified, guiding their development and efficient utilization.