Organic geochemistry of the British Kimmeridge Clay: 3. The occurrence and distribution of acyclic isoprenoid C19 alkenes in Kimmeridge Clay shale oils |
| |
| Affiliation: | 1. Western Australian Organic and Isotope Geochemistry Centre (part of The Institute for Geoscience Research), Curtin University, Perth, WA 6845, Australia;2. Geoscience Australia, Canberra, ACT 2601, Australia;3. School of Earth and Environment, The University of Western Australia, Perth, WA 6009, Australia;4. Murray Partners PPSA Pty Ltd, Perth, WA, Australia;5. CSIRO Energy, Sydney, NSW 2113, Australia;6. Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia;1. Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands;2. Institute for Risk Assessment Sciences (IRAS), Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands;3. IMARES – Institute for Marine Resources & Ecosystem Studies, Wageningen UR, P.O. Box 68, 1970 AB IJmuiden, The Netherlands;1. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, 430074 Wuhan, China;2. Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ), 14473 Potsdam, Germany;3. Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University Oldenburg, 26111 Oldenburg, Germany |
| |
| Abstract: | The occurrence and distribution of acyclic isoprenoid C19 alkenes (pristenes) in Kimmeridge Clay shale oils has been examined. Pristenes comprise ≈ 9 to 15% of isolated alkene fractions, and ≈ 8% of total shale oil non-aromatic hydrocarbons. They are generally much more abundant than pristane, possibly because only limited hydrogenation of isoprenoid alkenes occurs during pyrolysis. Two pristene isomers are identified (mass spectrometry, retention indices, g.c. co-injection), with prist-2-ene the more abundant in several Kimmeridge shale oils. Prist-2-ene/prist-1-ene ratios show some correlation with sediment oil yield and clay mineral content. Clay-rich low oil yield sediments often give prist-2-ene dominated shale oils, whereas high oil yield sediments show prist-1-ene dominance. Results suggest the conversion of prist-1-ene to prist-2-ene during pyrolysis by a time dependent, thermodynamically favourable double bond rearrangement. Two mechanisms are suggested for the generation of prist-1-ene, the primary pyrolysis product, from C20 units CC bonded to Kimmeridge oil shale kerogen: lt]o li](i) a thermolytic, radical induced tertiary hydrogen abstraction followed by homolytic β CC bond cleavage, or li](ii) in the presence of clay minerals, a clay catalysed carbonium ion route involving Lewis acid tertiary hydrogen abstraction and heterolytic β CC bond fission. Prist-1-ene double bond rearrangement is suggested to occur by a clay-catalysed ionic pathway involving proton-donor site double bond protonation followed by collapse of the resultant tertiary carbonium ion by Lewis base deprotonation. While rearrangement is likely to be retarded in analytical flash pyrolysis, Fischer pyrolysis conditions (and laboratory thermal maturation) allow more time for secondary rearrangement. Where the rate of rearrangement is enhanced by increased clay catalyst concentration, e.g. clay rich Kimmeridge shales, prist-2-ene becomes increasingly prominent in the resultant pyrolysates. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
