Study On The Sedimentary Facies And The Geochemical Character Of The Hydrocarbon Of Wufeng-Longmaxi Formation, Northeast Of Chongqing

Due to extensive development of marine black shale,the Upper Yangtze region has become China's leading area of shale-gas exploration and development.Located on the northern margin of the Yangtze,the northeast of Chongqing widely developed Wufeng-Longmaxi marine organic-rich shale.After the previous exploration and evaluation of oil and gas in the region by many times,it is held that this layer has a large potential to explore shale-gas.On the basis of study by predecessors,the essay measures and describes precisely,takes samples,as well as analyzes the shale gas parameter through carrying out outcrop sections.It has systematically studied the area's sedimentary faces of types of organic shale and its regional layout through applying sedimentology,petrology and organic geochemistry in an all round way.What's more,according to organic shale's hydrocarbon feature,the essay has added up the effective shale's thickness of each outcrop section.Combined with shale sedimentary and its layout character in the studying area,it has acquired the regional layout of effective shale in the studying area.In general,the conclusions mainly include the following aspects:?1?The rich-organic shale in the wufeng-longmaxi formation is mainly resulted by deep water shelf environment,whose lithology is mainly made up of black carbonaceous shale,siliceous mudstone,silty carbonaceous shale,silty mudstone and with little sedimentary tuff as well as includes abundant grapholite fossils,which are precipitated by occlusive and semi-occlusive stranded hydrostatic.The rich-organic shale is distributed in a large continuous area in the study area,whose thickness is about 40-80cm.According to geotectonic feature and regional construction-sedimentary evolution,it holds that the black shale in wufeng-longmaxi formation is the shallow shale sedimentary.What's more,in the light of the color of rock,the distribution of grapholites etc,it is further divided into deep-water shelf,shallow shelf sub-face and deep water shelf muddy,shallow muddy shelf,stucco shallow shelf micro-turbidite sedimentary.?2?According to the analysis to integrated sedimentary facies,tit's considered by two-dimensional distribution characteristics,and regional distribution characteristics of each typical section in study area that the layer of wufeng-longmaxi formation in northeast of Chongqing is relative stable.The middle of tian ba townlet and jian shan townlet of Wuxi county is the largest in shale thickness,reaching above 80m,being the deposition center of study area;the layer thickness away from the center position gradually reduces and it reduces to about 40m in shuang he country,Cheng kou county.Located in the northern study area,the bottom sedimentary shallow shelf phase of wufeng-longmaxi formation in the area of Miao ba townlet and Hou ping townlet is characterized by the transition between yellow gray marls of underlying linxiang formation and black mudstone of overlying longmaxi formation.Compared with deep-water shelf deposition of wufeng-longmaxi formation in the center area of tian ba townlet Wuxi county,it has some differences.As in the early period of wufeng,because of relatively higher altitude in the area of Miaoba-Houping,when it occurred transgression,the depth of water didn't increase rapidly but slowly.This indicates the area exists underwater ridges or palaeohigh;it has converted into deep-water shelf environment as longmaxi formation occurs large scale transgression.?3?It is considered that the wufeng-longmaxi formation shale of the study area has good hydrocarbon generating conditions with high organic carbon contents,whose TOC are generally bigger than 2%,the biggest approximately 7.56%,and averagely 3.09%;organic types are mainly the?kerogen,and the other parts are?₁;its maturity is much higher,Ro is generally greater than2%and the local part can reach 3%,and they basically belong to high mature-overmature.Based on above parameters,the thickness of effective shale in wufeng-longmaxi formation is between40-81.37m.The largest thickness in the area is tian ba and jian shan townlet of Wuxi county,reaching 81.37m,and the second largest is Miao ba and Hou ping townlet,above 70m.Effective shale's thickness gradually reduces from the area of tian ba townlet to the east and west sides,and it reduces to about 40m in shuang he country,Cheng kou county.In general,Effective shale's thickness spreads steadily and the northeast of Chongqing holds sound potential in shale gas.