Further comparison of methods for measuring kerogen pyrolysis rates and fitting kinetic parameters

We compare rates of product generation during pyrolysis of several petroleum source rocks and isolated kerogens by nonisothermal techniques, including Rock-Eval pyrolysis, condensed oil evolution, and pyrolysis MS/MS. We discuss problems related to temperature calibration in the Rock-Eval instrument, and confirm that standard Rock-Eval temperatures are in error by about 40°C. Calculations using Gaussian and discrete activation energy distributions and associated frequency factors derived from Rock-Eval data by nonlinear regression agree within a few °C with oil evolution at 2°C/min and pyrolysis-MS/MS at 4°C/min. This comparison also demonstrates that activation energy distributions are needed for oil alone as well as for gas and for total hydrocarbons from many source rocks. Discrepancies between Rock-Eval kinetics and oil evolution at 2°C/h and hydrous pyrolysis are related to mass transport limitations. Finally, we discuss the sensitivity of the extrapolation of reaction rates to geological conditions and how the extrapolation may be influenced by erroneous data or kinetic analysis.