The time-temperature-maturity relationship: A chemical kinetic model of kerogen evolution based on a developed molecule-maturity index

•A new maturity index of kerogen was proposed based on the changing molecular structure.•There is a positive linear correlation between the portion of oil/gas and MMI (the slope of this sample is 8.43).•The maturity-dependent activation energy (150 KJ to 350 KJ) was obtained.•Kerogen maturity evolution kinetic model was developed.•Choice of temperature and time by the equation can improve efficiency of artificial maturity. Kerogen maturity is an important indicator for evaluating source rocks. We propose a kerogen maturity index (molecule-maturity index, MMI) based on the changes in the molecular structure of organic matter during thermal evolution. The MMI has a positive correlation with vitrinite reflectance. Molecular dynamics simulations indicate that the weight loss is with a positive linear correlation with the MMI, demonstrating the ability of the index to reflect the hydrocarbon generation of organic matter. In addition, a new conversion is introduced by the MMI to analyze the kinetics of kerogen thermal evolution. The activation energy is expressed as a continuous function of the MMI linking by the new conversion. The activation energy was calculated at the isoconversional points of previous conversion, which was not defined as a continuous function before. A linear relationship between the activation energy of kerogen is observed, and a new chemical kinetic model of kerogen thermal maturity is established based on the MMI (kinetic model of the maturity evolution, MEKM). The MEKM equation has a simple form and is convenient for engineering applications. Our findings provide insights into the kinetics of kerogen thermal maturation and guide the choice of temperature and time for artificial maturity.