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Geological Characteristics Of Gas Shale In The Lower Cambrian Niutitang Formation Of The Upper Yangtze Platform

Posted on:2015-01-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:C LuoFull Text:PDF
GTID:1220330467467694Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
According to the different features of shale-gas of the Niutitang formation in theUpper Yangtze Block including the stratigraphy, geobiology, organic geochemistryand gas adsorption etc., we came to nine conclusions as follows:(1) The Lower Cambrian Niutitang Formation consists of mudstones, siltymudstone, siltstone and shale, siltstone, shale, calcareous mudrock and dolomiticmudrock etc, deposited under the littoral facies, shallow-water shelf, deep-water shelfand margin continental shelf from northwest to southeast.(2) There is a coupling relationship between the distribution of the Niutitangformation with TOC>2.0%and The distribution of Niutitang formation and thethickness of black shale of TOC>2.0%in western edge of Upper-Yangzi region arecontrolled by intracratonic sag which featured by thick deposition in central area anddiminishing from middle to the two sides. The formation and evolution of Mianyang-Changning intracratonic sag is explained through the comparative study ofstratigraphy and lithologic stratigraphy. The passive continental margin controls theeast side of the Upper-Yangzi region, making the isopach paralleled with that of thepassive continental margin. The strata thickness of shallow-water shelf is greater thandeep-water shelf’s. But the situation in thickness of TOC>2.0%black shale is incontrary.(3) The black shale of Lower Cambrian Niutitang formation in Upper-Yangziregion with good habitat type, high primary productivity, favorable redoxenvironment and high burial efficiency. In particular, the primary productivity in theshallow-water shelf is lower than that of in deep-water shelf.(4) The black shale in the Niutitang formation is with high organic contentranged from0.04%to15.31%, with type I. However, the maturity is high toover-mature stage.It is characterized with clay minerals (illite, chlorite, and a small amount ofmontmorillonite), quartz, feldspar, carbonate (calcite and dolomite), pyrite and apatiteof mudrocks in the Niutitang formation. There is a coupling relationship between themudrock mineral composition and location of the host rock. The deposits under the shallow-water shelf have less quartz content that those of deep-water shelf, however,the contents of clay, carbonate and feldspar of deposits show contrast way.(6) The Niutitang formation is characterized with primary intraparticle pore,Secondary intraparticle pore, mixed genetic intraparticle pore, primary intraparticlepore, Secondary intraparticle pores, mixed genetic intraparticle pore, organic pore andfracture. In which each type of pore consists of different skeleton component.(7) The black shale can be divided into five categories based on the isotherm,pore size distribution, pore volume and specific surface area. The first and secondcategories characterized with bioclastic siliceous rocks, carbonaceous mudstone, siltymudstone, muddy siltstone show better porosity than others.Bioclastic siliceous rocks, carbonaceous mudstone, silty mudstone, muddysiltstone in the first and second category have good porosity, the next is medium-coarse siltstone and the last are Hydrothermal siliceous rocks, siliceous mudstone,dense carbonaceous mudstone and dolomitic shale.Furthermore, the black shale located in the central and southeast of Guizhouprovince, western area of Hunan province and Hubei province and east Chongqinghas the best porosity than that in the Panzhihua-Xichang and east Yunnan province.The black shale of the southwest Sichuan Province is with worst porosity.(8) The adsorption capacity of siliceous rocks is1.83~2.92cm3/g with averagevalue of2.39cm3/g from six samples. Mudrock shows the strongest adsorptioncapacity with value of1.03~5.04cm3/g, and an average value of2.46cm3/g from54samples. In particular, the adsorption capacity of carbon mudstone is stronger thanthat of siltstone. The adsorption capacity of calcium rock has a wide variation rangewith1.56~2.89cm3/g, and an average value of2.09cm3/g from4samples.(9) The controlling model of adsorption capacity is tectonics framework controlsbasin development, basin development controls facies, facies controls primaryproductivity and mineral component. Primary productivity transformed intosedimentary organic matter and burial organic matter under the necessary condition ofredox. Influenced by external factors like temperature and pressure, sedimentaryevolution generates burial organic matter evolution and mineral componentconversion, finally the residual organic matter and mineral composition came intobeing. They controlled the pore volume and specific surface area in different level.Under the external factors of current temperature and pressure, the pore volume andspecific surface area exist in the end and control the adsorption capacity of black shalein reality.
Keywords/Search Tags:Gas-shale, Niutitang formation, geochemistry, reservoir, controlling factor, Upper Yangtze Platform
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