| Shale gas is a kind of very important unconventional natural gas resources,and its new theory of exploration and development,new technology and breakthrough of the production will be the highland competing among countries in this century.It is a special kind of strategic resource,which plays an important role in ensuring energy security and advancing economic sustainable development.This paper mainly aims at the mud shale of Longmaxi formation and Wufeng formation in the East Sichuan Wuling Mountain area.we find out shale gas dessert area by means of outcrop observation and analysis,the test of main and trace elements,the interpretation of seismic data,and the indoor mineral experiments of shale sample,comprehensive analysis of the geological conditions of shale gas accumulation.The study area has been subjected to multiple stages of tectonic uplift and denudation,forming a unique status of the topographic and geomorphic features,and full of fractures.In order to provide scientific basis for the exploration and development of shale gas in studied area,this paper mainly analyzes the sedimentary environment of shale and tectonic environment,spatial distribution,organic geochemical characteristics of hydrocarbon source rocks,reservoir space type,gas-bearing properties,and shale gas preservation conditions,etc.By field investigation and extensive stratigraphic correlation analysis,we found that the black shale of studied stratum developed widely.The distribution patterns of REE and trace element discrimination diagrams show that the sediment source is from the upper crust,and the sedimentary tectonic background is dominated by the passive continental margin.The analysis of sedimentary facies and geochemical elements indicate that the black shale is mostly developed in anoxic environment,and has high productivity and hydrocarbon generation potential.The upper Ordovician Wufeng Formation is mainly dominated by slope facies,while Lower Silurian Longmaxi Formation is mainly consisted by deep shelf-shallow shelf facies,and deep shelf facies are favorable sedimentary environment.Shale from Longmaxi Formation is mainly distributed in the bottom place,plane distribution from North West to south east direction gradually thickening,Xishui-Tongzi and Xiushan-Youyang area are the center of subsidence,with the thickness of 60~120 meters.The overall depth of shale in the study area is among 1500~4500 meters.The best buried depth is among 2500~3500 meters,and the advantages of regional concentration is distributed mainly over northern regions of Guizhou,from Zheng'an to Daozhen area.The parent rock of organic matter comes from lower aquatic organisms,and the organic matter type is mainly composed of kerogen type I and type ?1.The abundance of organic matter varied greatly.and the range of TOC was from 0.11% to 5.04%,with an average value of 1.88%.Ro between 2% to 4%,the degree of thermal evolution are from the overall high to over mature stage.and the shale shows good geochemical characteristics.The porosity and permeability are very low,belonging to the super low permeability gas reservoir type.The gas content dates from field analysis experimentis are most less than 1 m3/t,while gas content from isothermal adsorption experiment are between 1.53 m3/t ~4.76 m3/t,which shows good adsorption capacity.A variety of seismic attributes are used to identify the fracture development zone,which is the favorable position for the development of shale gas reservoirs.By drawing plane contour maps of shale thickness,total organic carbon content,maturity,burial depth,we use multi factors superposition method to select Xishui-Tongzi-Zhengan and Xiushan-Youyang-Xianfeng favorable areas as shale gas potential area. |
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