Thermal simulation experiments of kerogen samples show that free radical concentration would first increase and then decrease along with increasing thermal evolution degree of kerogen samples.The increase of free radical concentration is related to the ruptare of alkyl radical side chain and dropout of heteroatomic functional group in lower evolutionary phase of kerogen;while the decrease of free radical concentration is the results of condensation and polymerization of kerogen during higher evolutionary phase.The free radical concentration is controlled by temperature and heating time

thus the experimental data can be used to establish quantitative relational expression between free radical concentration of kerogen and temperature-time index.The theoretically calculated values of free radical concentration should be fitted with the measured values by repeatedly adjusting denudation thickness and heat flow values

the inversion of thermal history of carbonate strata can thus be made.Since there are only a small amount of thermal simulation experimental data can be used in this study

the result achieved in this study is just for exploring a new methodology

and the scope of application is limited.Thermal simulation experiments and corresponding researches on kerogen samples from marine carbonates should further be carried out in the future.