Kinetics of petroleum generation and cracking by programmed-temperature closed-system pyrolysis of Toarcian Shales

Primary kerogen-to-petroleum and secondary oil-to-gas conversion processes in marine source rocks have been studied contemporaneously by programmed-temperature closed-system (MSSV) pyrolysis of Toarcian Shale concentrates at heating rates of 01,0.7 and 5.0K min(-1) in the temperature range of 300-610 degrees C. All pyrolysates were analysed by single-step on-line gas chromatography. The cumulative evolution profiles of liquid and gaseous compounds were deconvoluted into generation curves for oil (C(6+)), primary gas and secondary gas using complementary open-system experiments and simple stoichiometric relationships. The subsequent kinetic analysis resulted in potential versus activation energy distributions which turned out to be comparatively broad for oil and primary gas and rather narrow for secondary gas, indicating that the formerer are generated from more inhomogeneous precursor materials than the latter. The dominant activation energies were found to increase from 52 (217.9) (oil) to 53 (222) (primary gas) and 55 (230.5) kcal mol(-1) (kJ mol(-1)) (secondary gas); the best-fit frequency factors were calculated around 1015 min(-1). By extrapolation to a geological heating rate of 5.3K my(-1) (10(-11) K min(-1)) the onset of oil generation is predicted to occur at 90 degrees C, the maximum oil formation rate at 140 degrees C and the onset (peak generation) of primary and secondary gas at 110 degrees C (165 degrees C) and 150 degrees C (180 degrees C), respectively. (C) 1997 Elsevier Science Ltd.