Assessing the overlap of primary and secondary reactions by closed- versus open-system pyrolysis of marine kerogens

• Published in: Journal of analytical and applied pyrolysis Vol. 56; no. 1; pp. 33 - 46
• Main Authors: Dieckmann, V, Schenk, H.J, Horsfield, B
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2000
• Subjects: Closed- and open-system pyrolysis; Marine kerogens; Micro-scale vessel technique; Closed- and open-system pyrolysis; Micro-scale vessel technique; Marine kerogens
• ISSN: 0165-2370; 1873-250X
• DOI: 10.1016/S0165-2370(00)00083-8

The evolution of various petroleum fractions during programmed-temperature pyrolysis of immature samples from the Toarcian Shale (Germany) and the Duvernay Formation (Canada) at a heating rate of 5.0 K min
−1 has been studied comparatively under closed- and open-system conditions using the micro-scale sealed vessel (MSSV) technique in the former and a modified MSSV technique in the latter case. Whereas open-system heating gives raise to continuous primary product generation, closed-system experiments are marked by the overlap of primary generation and secondary cracking reactions; the apparent degree of overlap, however, turns out to be different for different compound classes. Primary generated C
15+ (total C
15+ fraction) compounds, in particular, are subjected to severe secondary cracking from the beginning. However, at temperatures lower than 460°C for both samples, secondary cracking essentially transforms C
15+ compounds into C
6–14 (total C
6–14 fraction) compounds. Because these processes take place only within the C
6+ fraction the sum of closed-system C
6+ compounds is close to the quantities of C
6+ compounds generated in the open-system. At temperatures higher than 460°C secondary oil-to-gas cracking becomes obvious from the decrease of C
6+ concentrations. Because the open-system generation of C
6+ compounds has come to an end at this temperature, the overlap of primary and secondary reactions only affects the overall composition of the C
6+ fraction in the closed-system but not the timing of secondary gas formation.