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Xu J.,Jilin University | Xu J.,University of Leoben | Xu J.,Key Laboratory for Oil Shale and Paragenetic Energy Minerals | Bechtel A.,University of Leoben | And 7 more authors.
International Journal of Coal Geology | Year: 2015

In the well-known continental Songliao Basin, the oil shale successions of the Cretaceous Qingshankou Formation are excellent source rocks for oil. The oil shale layers with high TOC (total organic carbon) contents developed at the bottom of the formation. They are divided into the lower oil shale (TOC up to 18.3%) and the upper oil shale layer (TOC up to 14.4%). The oil shale layers and accompanying mudstones are investigated by high resolution analyses of drill cores by pyrolysis, organic petrology, organic and inorganic geochemistry. The results demonstrate the predominance of type-I kerogen derived from algal-microbial mats (i.e. lamalginite). However, increased proportions of plant-derived organic matter are indicated by Rock-Eval parameters and the presence of vitrinite in the upper oil shale. As evidenced from lower concentrations of hopanes, higher sinking rates of organic matter (OM) are suggested to have been responsible for a lower extent of microbial degradation during accumulation of the lower oil shale unit. The environmental conditions are characterized by anoxic saline bottom water overlain by an extended zone of freshwater, favorable for OM production and preservation. Under these preconditions, oil shale thickness and quality are governed by primary productivity, related to accommodation space and nutrient supply. Redox conditions within the water column are the key factor controlling organic matter preservation. © 2015 Elsevier B.V.

Xu J.,China University of Petroleum - East China | Xu J.,University of Leoben | Liu Z.,Changchun University | Liu Z.,Key laboratory for Oil Shale and Paragenetic Energy Minerals | And 9 more authors.
International Journal of Coal Geology | Year: 2015

The controlling factors of oil shale formation within the Upper Cretaceous Qingshankou and Nenjiang Formations of the Songliao Basin are investigated by petrological and geochemical methods. Sediment deposition was balanced by basin subsidence, resulting in the accumulation of Cretaceous strata of high thickness. Global sea level fluctuations have been related to periods of oil shale deposition within the basin. The results indicate a comparable depositional environment during oil shale formation within the two Upper Cretaceous strata with respect to palaeotectonic and palaeoclimate, but differences in the accommodation space during accumulation of the two formations. The larger accommodation space during deposition of the Nenjiang Formation resulted in the higher thickness and wider distribution of the oil shale members (total thickness: 11.2-32m; distribution area 4.48×103km2) within the basin, as compared to the oil shale of the Qingshankou Formation (total thickness: 2-19.3m; distribution area 1.3×103km2).Further differences exist with regard to the palaeoenvironment of oil shale formation and primary productivity. Deposition of the Qingshankou Formation 1st member and Nenjiang Formation 1st member took place within a saline-brackish lake under anoxic conditions in the bottom water. Preservation of organic matter is suggested to have been less favorable during deposition of the Nenjiang Formation 2nd member. Higher primary productivity is believed to be the responsible factor for the accumulation of organic-rich sediments in the Qingshankou Formation 1st member. The interplay of these two factors (i.e. preservation, productivity) leads to the formation of oil shale in the Qingshankou Formation (average TOC: 8.32%; TOCmax: 13.52%; average oil yield: 5.57%/) with better hydrocarbon source rock potential and slightly higher oil yield during pyrolysis as in the Nenjiang Formation (average TOC: 7.76%; TOCmax: 9.7%; average oil yield: 5.54%).Primary productivity is suggested as the main controlling factor on differences in oil shale quality and source rock potential between the two formations, whereas the variations in quality within each formation mainly depend on the preservation of organic matter. The high thickness, wide spatial distribution and excellent hydrocarbon potential of the Upper Cretaceous oil shales in the Songliao Basin are suggested to have been the result of large accommodation space, stable palaeoenvironmental conditions, and high primary productivity. © 2015 Elsevier B.V.

Zhang M.,Jilin University | Liu Z.,Jilin University | Liu Z.,Key Laboratory for Oil Shale and Paragenetic Energy Minerals | Qiu H.,Oil and Gas Resources Strategic Research Center | Xu Y.,Oil and Gas Resources Strategic Research Center
Oil Shale | Year: 2016

Analysis of the abundance and type of organic matter of oil shale in the sequence stratigraphic framework of the Middle Permian Lucaogou Formation at the northern foot of Bogda Mountain, NW China, was carried out. The Lucaogou Formation consists of two well-completed 3rd order oil shale sequences, sequence 1 and sequence 2. With respect to organic matter abundance, in each sequence, the TOC of oil shale in the lowstand systems tract (LST) and the regressive systems tract (RST) is of medium abundance. The TOC of oil shale in the transgressive systems tract (TST) is of higher abundance, and in the highstand systems tract (HST), of highest. In regard to type, the organic matter of oil shale in the LST of either sequence is mainly of type II2 or type II1. In TST and HST, it is predominantly of type II1 and type I, respectively, and in RST, of type II1 or II2. The proportion of lake algae in the organic matter of oil shale is the highest in HST, while the share of terrestrial plants is the highest in LST and RST. Being originated from lake algae and terrestrial plants, the organic matter of oil shale in TST is of mixed type. © 2016 Estonian Academy Publishers.

Meng Q.-T.,Jilin University | Meng Q.-T.,Key Laboratory for Oil Shale and Paragenetic Energy Minerals | Meng Q.-T.,Key Laboratory for Evolution of Past Life and Environment in Northeast Asia | Liu Z.-J.,Jilin University | And 9 more authors.
Zhongguo Shiyou Daxue Xuebao (Ziran Kexue Ban)/Journal of China University of Petroleum (Edition of Natural Science) | Year: 2012

Based on the geochemical research of mudstone and oil shale of Huadian formation, the productivity of Eocene Paleo-Huadian lake was qualitatively and quantitatively recovered by using the organic carbon method, and the water environments, paleoproductivity change during the lake evolution and enrichment mechanism of organic matter were discussed. The results show that the evolution order of paleoproductivity in Huadian Basin is middle oil shale member, upper coal member and lower pyrite member. The highest paleoproductivity achieves at 1 033.09 g/(m2·a) during the sedimentary period of middle member of Huadian formation. The ancient lake is in eutrophic state. The bacteria and algae are dominate in organic matters and the lake water is in steady hypoxic and fresh-brackish reduction environment during this stage, which reflects that the high paleoproductivity is mainly contributed by algae and directly influences the origin and abundance of organic matters. The alternative salinity change of lake water makes the bottom water be in a steady hypoxic environment, which is a favorable environment for organic matter conservation. The lakes during the lower member and upper member of Huadian formation are in obvious mesotrophic state and fresh hypoxic environment, and the average paleoproductivity is 143.82 g/(m2·a) and 153.26 g/(m2·a) respectively. High paleoproductivity is the first condition for organic matter enrichment of oil shale, and steady hypoxic environment in bottom water is the most favorable environment for organic matter enrichment.

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