Study On Source Rocks Characterstics Of The Middle Jurassic In Qilian Permafost

Recent years,the gas hydrate samples were obtained in Qilian Mountain permafrost,Qinghai,Northwest China.This discovery is a historical breakthought in the gas hydrate exploration of the permafrost areas in China.The geological structure of this area is complicted,the natural gas hydrate samples mainly occur in the sandstone porosity and shale fractures of Jiangcang formation of Jurassic series.In the natural gas hydrate stability zone is also found some oil sand,and the oil level,is from the oil immersed,oil patch to the oil stains.In order to understand the source of crude oil in the oil sands,we made the analysis and comparison research for the Middle Jurassic coal-measure source rock and lacustrine source rock,it also can provide a basis for the gas sources analysis of natural gas hydrate.Through drilling core analysis and combine the reseach of outcrop section and the theories of petroleum geology,sedimentology,etc,trace element analysis and combine the data analysis of drilling cores,analyze the Qilian Mountain Permafrost ancient Jurassic sedimentary environment.Then we made some analysis and evaluation for the Middle Jurassic coal-measure source rock and lacustrine source rock and discusses the hydrocarbon source of oil-bearing sandstone hydrocarbon.We obtain the following understanding:1.By analyzing microelements,during Jurassic deposition period,the deposition al environment is mainly continental lake environment.The analysis of Geochemistr y shows that the Jurassic source rock generally belongs to broad Semi-reduced half-o xidized depositional environment of freshwater,little of it belongs to brackish water environment.2.Based on core and outcrop data and together with particle size analysis,this study draws an conclusion that the major facies in Middle Jurassic of Muli area in the South Qilian basin consist of braided river,braided river delta and lacustrine facies,with local sublacustrine fan developed.3.Through the analysis of geochemical,the lake facies mudstone and oil shale of the Middle Jurassic in Muli area contain high organic matter abundance,but the organic matter abundance of carbonaceous mudstone and coal is not high.The organic matter type of lake facies mudstone and oil shale is mainly type I and type ?,carbonaceous mudstone and coal is type ?.The subject of hydrocarbon source rock at the mature stage and a small amount of in high mature stage.4.Oil-source correlation shows that the crude oil in Muli drilling oil sands has two sources,one from the Middle Jurassic lacustrine source rocks,and the other may be derived from the deep Carboniferous or Triassic coal source rock.