Based on the pyrolysis, kinetic model of the stable carbon isotope of the methane is a very useful tool for studying nature gas generation and evaluation. Here, some models are reviewed and the advantage and shortcomings of these models are analyzed in brief. All these models can be divided into two types. One is based on Raleigh fractionation model. These models take the ratios of methane carbon isotope as results of fractionation. Calculating the fractionation factor is the important part in the models. The other model gives much more attentions to the results of the experiment. In the latter, methane is taken as two different products from different methane-generation groups. The kinetic parameters of every species (12C-and 13C- methane) is calculated, respectively, to simulate individual generation process. Then, the two species generation processes are combined to model the variance in methane isotope composition under geologicalcondition.
From our own experimental, the carbon isotope values of methane degrading from coal shows very complex trend. At the stage of low temperature, the isotope values become lighter, then become heavier and heavier with temperature, which may be related to heterogeneous source rock.
For the study of kinetics model about methane carbon isotope ratios, some issues do pay to further study, including ①Common pyrolysis experiment on coal is carried out at the temperature range between 300 and 600℃. As shown above, it is not enough to evaluate the carbon isotope variance of coal-derived methane. ②Overpressure occurs almost in the two thirds of sediment basins on the Earth. It is worth to further study how to model the effect of pressure on methane carbon isotope ratios. ③Episodic expulsion of hydrocarbon has been commonly accepted under geological condition. However, the effect of episodic expulsion on the natural gas component and carbon isotope composition can't be understood clearly. It is necessary to further study.