Study On Geochemical Characteristics Of Tight Oil And Reservoir Oil-bearing Property In Jimusar Depression

The Lucaogou group of Permian series in Jimusar depression in Junggar Basin is an important area of tight oil exploration currently.The thesis applies geochemical methods to study reservoir oil-bearing property,oil properties,sources of oil and gas,migration and accumulation mechanism of tight oil.The distribution of tight oil dessert are predicted and the enrichment conditions of tight oil are summarized.Geochemical parameters of reservoir tight oil-bearing property including S1,S1/TOC,chloroform bitumen A,TPI,S1/S2.The criteria of tight oil dessert of Lucaogou group in Jimusar depression are established as follows:S1/TOC>100(mg oil/gTOC),S1>10mg/g,TPI>0.12,S1/S2>0.22,chloroform bitumen A>0.7%.The reservoir tight oil-bearing property is related to lithology,sedimentary facies,source rock expulsion and oil migration,porosity and permeability.Oil-bearing property of siltstone,dolomite,dolomitic mudstone and silty mudstone reservoirs are good,while oil-bearing property of pure shale reservoirs are poor.The larger reservoir porosity and permeability,the better the reservoir oil-bearing property.Semideep lacustrine facies is conducive to the formation of tight oil reservoir with large thickness and abundance of oil.Migration and concentration of tight oil cause hydrocarbon in reservoirs and oil-bearing abundance increasing,with high S1/TOC and low Tmax.Hydrocarbon expulsion of source rocks cause the content of residual hydrocarbon and oil-bearing abundance reducing,with low S1/TOC and high Tmax.The upper and lower dessert possess maximum thickness in center of the depression predicted by Logging.Maximum thickness of the upper dessert is 77 meters and under dessert is 73 meters.Mudstone and dolostone of Lucaogou group are important hydrocarbon source rocks.Maceral composition is mainly sapropelinite.Source rocks are high quality with high abundance of organic matter.The different sources of crude oil of upper and lower dessert make the difference of oil property.Crude oil and soluble organic matter in reservoirs are detected a large number of ?-carotene.It shows quality source rocks of Lucaogou group sedimentary environment is saltwater reducing environment.Reservoir with high oil abundance and extract with chloroform bitumen A are from high-quality source rocks of upper and lower dessert respectively.In addition,characteristics of biomarker fingerprint are different between a very small part extract and crude oil.Usually this kind of extract with low chloroform bitumen A content and weak oil and gas shows are not originated from the main source rocks.There is an obvious close migration phenomenon of tight oil.Oil enriched in siltstone,dolomite,dolomitic mudstone and silty mudstone.Shale and dolomite are high-quality source rocks.Tight oil from Lucaogou group enrichment conditions are as flollows:1)The source rock is in the mature stage with large thickness and high abundance of organic matter.2)Reservoir porosity and permeability are relatively large and oil saturation of reservoir is high.3)Mudstone interbedded with dolostone.Configuration condition of reservoirs and source rocks is good.