Comparison of methods for measuring kerogen pyrolysis rates and fitting kinetic parameters

We determine rates of product evolution during pyrolysis of several petroleum source rocks and isolated kerogens by nonisothermal techniques, including Rock Eval pyrolysis and pyrolysis-MS/MS. The resulting data are analyzed by nonlinear regression and simpler correlation techniques in terms of discrete and Gaussian distributed activation energy models. We find that temperatures measured by standard Rock Eval analysis are too low by about 40°C, resulting in kinetic expressions that are much too fast. Proper temperature calibration eliminates this problem. We explore the sensitivity of the kinetic parameters and extrapolation to geologic heating rates to uncertainty in the temperature calibration. We find that the discrete distribution model provides a superior fit to the laboratory data and probably a more reliable extrapolation to geological heating rates. We also assess how differences among kinetics for individual species relate to the activation energy distributions required for total hydrocarbon evolution. Kinetics from Rock Eval pyrolysis predict hydrocarbon generation rates intermediate between kerogen decomposition and oil expulsion during hydrous pyrolysis, but slight differences in activation energies result in similar predictions for a geological heating rate. Predictions for type I kerogens fall at the high end, but within the range, of oil generation temperatures predicted for type II kerogens.