Effect of Uncertainty of the Pre‐Exponential Factor on Kinetic Parameters of Hydrocarbon Generation from Organic Matter and its Geological Applications

AbstractThe source rock sample of the Shahejie Formation (upper Es4) in Jiyang Sag was pyrolyzed under open system with the Rock‐Eval‐II apparatus, and then kinetic model parameters were calibrated for investigating the effect of uncertainty of pro‐exponential factors on kinetic parameters and geological applications, where the parallel first‐order reaction rate model with an average pre‐exponential factor and discrete distribution activity energies was used. The results indicate that when the pre‐exponential factor changes from low to high, an extreme value for residual errors occurs. And with the increasing pre‐exponential factor, the distribution shape of activation energies are nearly the same, but the values of activation energies move higher integrally, and the average activation energy increases about 12 kJ/mol for every 10‐fold of the pre‐exponential factors. Extrapolating the geological heating rate of 3.3 °C/Ma, the results show that with the increases in pre‐exponential factor, the geological temperature corresponding to TR0.5 (transforming ratio of hydrocarbon generation is 50%) increases gradually, and the additional temperature gradually decreases. Combined with geochemical data of source rock, the kinetic parameters with different pre‐exponential factors are used to calculate the transformation ratio of hydrocarbon generation, and the result indicates that kinetic parameters corresponding to the better optimized pre‐exponential factor are more suitable. It is suggested that the risk assessment of hydrocarbon generation kinetic parameters should be enhanced when using the kinetic method to appraise the oil‐gas resources. Meantime, the application result of different kinetic parameters should be verified with geological and geochemical data of source rock in the target area; therefore, the most suitable kinetic parameters for target can be obtained.