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Yu Y.-X.,CAS Institute of Geology and Geophysics | Yu Y.-X.,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: 2016

Amounts of silty laminae in continental shale gas reservoir were investigated for the Zhangjiatan shale of Yanchang Formation,Ordos Basin.The purpose of this study is to provide awareness of the nature and discrepancies in pore structure between the silty laminae and clayey laminae.By separating the silty laminae from the shale core mechanically,a combination measurement series of mercury injection capillary pressure,N2 adsorption and carbon dioxide adsorption were performed on the two parts.An integrated pore size distribution covering pore diameter range of 0.1nm-100μm was obtained by using appropriate sample particle size and calculation model.The comparative analysis of pore structure shows that the clayey laminae are dominated by mesopore and micropore while the silty laminae are dominated by macropore.The pore volume distribution in clayey laminae can be sorted as mesopore>micropore>macropore while in silty laminae it is macropore> mesopore>micropore.The average total pore volume is 2.02m3/100g for silty laminae and 1.41m3/100g for clayey laminae The porosity of silty laminae is 5.40%,which is larger than that of clayey laminae 3.67%.Since the silty laminae have larger pore width and pore space,they are more permeable and porous than the clayey laminae and can act as favorable conduits and reservoirs for shale gas. © 2016, Science Press. All right reserved.


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.


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.

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