Organic geochemistry and petrography of Lower Cretaceous Wealden black shales of the Lower Saxony Basin: The transition from lacustrine oil shales to gas shales |
| |
| Institution: | 1. Institute of Geology and Geochemistry of Petroleum and Coal, Energy and Mineral Resources Group (EMR), RWTH Aachen University, Lochnerstr. 4-20, 52056 Aachen, Germany;2. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Research and Development Research Institute, Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China;4. School of Environment and Energy, South China University of Technology, Guangzhou 510006, China;5. Dongguan Environmental Monitoring Centre Station, Dongguan 523000, China;1. Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia;2. National Centre for Petroleum Research and Development, A.T.B.U, PMB 0248, Bauchi, Nigeria;3. Geology Department, Faculty of Applied Science, Taiz University, 6803 Taiz, Yemen;4. Department of Geology, Ekiti State University, P.M.B. 5363, Ado-Ekiti, Nigeria;1. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;3. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;4. Key Laboratory of Natural Resource of the Changbai Mountain and Functional Molecular of Ministry of Education, Yanbian University, Yanji 133002, China |
| |
| Abstract: | Ninety-seven Wealden black shale samples from three wells in the Lower Saxony Basin have been studied by organic geochemical and organic petrographical methods to determine their maturity, organic facies and depositional environment. The maturities of the three wells range from early mature (Ex-A), late to postmature (Ex-C) to overmature (Ex-B) as determined by vitrinite reflectance measurements, diamondoid ratios and other geochemical maturity parameters. Ex-C and Ex-B show distinct petrographic features related to oil generation and migration. In particular, the occurrence of dispersed solid bitumen replacing initial type I kerogen suggests a formerly active petroleum system. Structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity. A freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well. These alginites are absent in the more mature gas shales of wells Ex-C and Ex-B. Geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters, while the occurrence of β-carotane in some samples indicates events of increased salinity, although no hypersaline conditions are inferred due to very low gammacerane indices. Increased amounts of vitrinite and inertinite in samples of Ex-B suggest locally significant terrigenous input of organic matter for some periods during Wealden Shale deposition. High sulfur/organic carbon ratios provide evidence for sulfate rich waters and (partly) anoxic bottom water conditions. While the lower mature lacustrine source rocks generate paraffinic/waxy oils, gas and condensates are produced at post-mature stages. Furthermore, maturity distribution maps from 3D numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
