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Zheng Y.-D.,China University of Petroleum - East China | Lei Y.-H.,CAS Institute of Geology and Geophysics | Zhang L.-Q.,China University of Petroleum - East China | Wang X.-Z.,Research Institute of Shaanxi Yanchang Petroleum Group | And 12 more authors.
Natural Gas Geoscience | Year: 2015

Shale thickness, total organic carbon content, brittle mineral content and physical property are key parameter of shale reservoir evaluation, which are obviously controlled by the sedimentary environment. Therefore, it's significant to study the sedimentary environment and the evolution of the shale formation about gas reservoir evaluation and desserts prediction. This paper systematically tested more than 40 element concentrations of 525 groups of samples in Zhangjiatan shale drilled by well Y1 in the South-Central Ordos Basin. Then we analyzed the evolution of the paleoclimate, the paleobathymetry, the paleosalinity, the paleoproductivity and the oxidation-reduction states of sedimentary environment. The results showed that there are significant periodical changes of the element concentrations and ratios of Zhangjiatan shale from bottom to top, indicating that Zhangjiatan shale was deposited in a warm and humid, freshwater-brackish, hypoxia sedimentary environment, between which, the IV unit was deposited in a wet sedimentary environment, when the water was deepest and highest reducing with high paleoproductivity. ©, 2015, Science Press. All right reserved. Source


Cheng M.,CAS Institute of Geology and Geophysics | Cheng M.,University of Chinese Academy of Sciences | Luo X.-R.,CAS Institute of Geology and Geophysics | Lei Y.-H.,CAS Institute of Geology and Geophysics | And 11 more authors.
Natural Gas Geoscience | Year: 2015

The Zhangjiatan shale of the Lower Chang 7 member of Yanchang Formation, Ordos Basin is an important exploration target for shale gas. Since the silty beds/laminae in the shale play an important role in gas storage, fluid flow, fracturing and development of shale gas/oil, it is of great significance to ascertain the thickness and the distribution characteristic of the silty beds/laminae. The measurement results from outcrop, core and thin section show that the silty beds/laminae have larger detrital grains than those in the clayey laminae and the silty laminae thickness mainly ranges from 0.5mm to 8mm. Their total thickness can occupy 7%-26% of the shale formation with an average density of 8-40 layers/m, which shows strong vertical heterogeneity. The thickness distribution of silty beds/laminae presents a fractal distribution on a dm to mm scale and the fractal dimension D has scale invariance over the whole thickness range. According to the data from the relatively thick layers of silty beds, the accumulative number of the thinner silty beds/laminae was estimated using the Number-size model. The accumulative thickness of silty beds/laminae and its ratio to the shale formation thickness were calculated. It has been verified that this method can ascertain the thickness of the silty beds/laminae effectively. ©, 2015, Science Press. All right reserved. Source

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