Hydrocarbon Generation Kinetics of Continental Organic Matter across Distinct Organic Matter Types

This study selected typical samples from major oil and gas basins in China and conducted open-system thermal simulation experiments. Based on experimental data, kinetic parameters were calibrated using parallel first-order reaction and overall n-order reaction models, revealing the kinetic characteristics of hydrocarbon generation from different types and maturity levels of organic matter (OM), and the kinetic characteristics of OM generation from different components. The results indicate that (1) Type I OM has the shortest hydrocarbon generation period (EasyRo = 0.50∼1.22%), Type II1 OM has a hydrocarbon generation period between 0.31∼1.22% EasyRo, and Type II2–III OM has the longest hydrocarbon generation period (EasyRo = 0.43∼2.58%). A large standard deviation (σ) of activation energy and a small reaction order (n) both indicate a less complex hydrocarbon generation reaction process. The proportion of gaseous hydrocarbons gradually increases, while the proportion of liquid hydrocarbons gradually decreases in the hydrocarbon generation components of OM from Type I to Type II2–III. (2) As the maturity of OM of the same type in the same basin increases, the starting temperature of hydrocarbon generation also increases, and the activation energy at the beginning of hydrocarbon generation increases. At the same time, the proportion of gaseous hydrocarbons is higher and the proportion of liquid hydrocarbons is lower in the hydrocarbon products generated from OM with higher maturity. (3) The gaseous hydrocarbons (C1–5) exhibit the longest generation period and the most dispersed activation energy distribution, with the highest n (average 2.29), indicating a complex gas generation process involving diverse parent material types. In contrast, the formation of heavy hydrocarbons (C14+) shows the most concentrated activation energy distribution and the lowest n (average of 1.37), reflecting a relatively homogeneous composition of the parent material types.