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

• Published in: Fuel (Guildford) 1998, Vol.77 (1), p.23-31
• Main Authors: Dieckmann, V., Schenk, H.J., Horsfield, B., Welte, D.H.
• Format: Article
• Language: English
• Subjects: Applied sciences; compositional kinetics; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; Geology and geochemistry. Geological and geochemical prospecting. Petroliferous series; in-source oil-to-gas cracking; non-isothermal closed-system pyrolysis; primary versus secondary gas; Prospecting and exploration; Prospecting and production of crude oil, natural gas, oil shales and tar sands
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/S0016-2361(97)00165-8

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 0.1, 0.7 and 5.0K min −1 in the temperature range of 300–610°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 −11K min −1) the onset of oil generation is predicted to occur at 90°C, the maximum oil formation rate at 140°C and the onset (peak generation) of primary and secondary gas at 110°C (165°C) and 150°C (180°C), respectively.