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

The source rock sample of the Shahejie Formation (upper E s4) 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. [ABSTRACT FROM AUTHOR]