首页|Quartz Cementation in the Lower Paleozoic Shales,Middle Yangtze Region,South China:Implications for Shale Reservoir Properties
Quartz Cementation in the Lower Paleozoic Shales,Middle Yangtze Region,South China:Implications for Shale Reservoir Properties
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As one of the most important constitutes of shales/mudstones,quartz has received in-creasing interests in the last decades,because productive shale gas successions are generally rich in quartz content.This study critically documents quartz types,silica source for quartz cementation and effect of quartz cementation on reservoir quality in the Lower Paleozoic shales,Middle Yangtze region,South China,including the Lower Cambrian Niutitang Formation and the Upper Ordovician-Lower Silurian Wufeng-Longmaxi formations.Our results suggest that high-resolution scanning electron mi-croscopy combined with cathodoluminescene techniques are necessary for identifying quartz types in shales.Integrations of high-resolution imaging technique and detailed geochemical analysis are able to document silica source for quartz cementation and silica diagenetic processes.Six types of quartz can be identified in the Paleozoic shales,primarily including detrital quartz silt,siliceous skeletons,quartz overgrowth,microcrystalline quartz(matrix-dispersed microquartz and aggregated microquartz),sili-ca nanospheres and fracture-filling quartz veins.Dissolution of siliceous skeletons provides the princi-pal silica sources for authigenic quartz formation in the Paleozoic shales.Authigenic quartz has dual ef-fects on porosity development.Quartz overgrowth definitely occupies interparticle pores and possibly squeeze spaces,whereas aggregated microquartz can form rigid framework that is favorable for gener-ating and preserving intercrystalline pores and organic pores.
shale gasquartzshale reservoir propertiesPaleozoic shalesMiddle Yangtze region
Tian Dong、Jian Gao、Shuangjian Li、Chuan Wang
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State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development,Beijing 102206,China
SINOPEC Key Laboratory of Geology and Resources in Deep Stratum,Beijing 102206,China
School of Earth Resources,China University of Geosciences,Wuhan 430074,China
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