Research On The Characteristics Of Jurassic Yan'an Formation Reservoir Of Yizheng-Wubu Of Zhidan Exploration Area

Ordos Basin is the second largest basin in China,Yan'an formation of Middle Jurassic in Ordos Basin is a major oil and gas department,Which was formed in the steady sedimentation period after the Late Triassic Indo-Chinese Movement,with the thickness of the formation of stable,distinct characteristics of a river delta system.Yizheng-Wubu area locates in the middle of Shanbei Slope Belt in Ordos Basin and the oil-bearing layers of Jurassic are mainly member 10-8 of Yan'an formation.The purpose of this paper is to study the reservoir characteristic of Yan'an formation in Yizheng-Wubu area,and then pointed out the main factors controlling hydrocarbon accumulation.Based on the fine stratigraphic correlation,combined with the rock types and their characteristics,structure and sedimentary structures,paleontology and well logging,the sedimentary systems of Yan'an formation had fluvial system and the delta system.The Yah 10 was typical braided river channels-filling type deposition,Yan 9～Yan 7 were delta plain facies.The river of research area mainly came from the west and the northeast,finally, outflow from the research area.According to a large number of rock cores and rock flakes,we think that the reservoir lithology of Yan'an formation mainly were medium-grained feldspathic lithic quartz sandstone with the particle size getting finer from lower to upper.The main diagenesis of the study area were compaction,pressure solution,cementation,dissolution and so on,the reservoir diagenesis of the research area had reached late diagenesis A period.The study area of Yan'an main types of rock porosity were primary intergranular porosity and dissolution porosity,which accounted 81.9%Of areal porosity.The average values of reservoir porosity was 14.6%,and the average value of reservoir permeability was 31.34×10^-3μm²,the composition type of pore throat mainly were middle hole middle throat-small throat.Because of bigger granularity,the physical of Yan10 were best among Yan10～Yan7,and the physical property of Yan 7 was worst.The high porosity -high permeability zone have a good reltionship with distribution pattern of sandstone in plane, the sedimentary and diagenesis affected the physical properties and unhomogenenity of the reservoir.Based on the physical properties,sheets information,sedimentary facies zone, sandstone body distribution etc,according to the classification standard,which was proposed in 2001 by mou zehui,a comprehensive evaluation of the reservoir has been made:Reservoir of Yan7 mainly belongs to typeâ…¢(that is poor quality reservoir);while reservoir Yan8-Yan10 mostly belong to typeâ…¡(that are medium quality reservoir).Synthetizing the reservoir quality,trap types,the sedimentary facies,the sealing ability of cap rock,etc.factors of controlling accumulation as follows:The deep～semi-deep lake mudstone of chang7 formation provided the high quality source rock for the oil accumulate ion,pre-Jurassic deep down-cutting river offered the migration pathway;the sedimentary facies decided the favorable oil reservoirs zone;the upper mud cap rock and side block of mudstone were essential to the accumulation;matching of nosing and difference compaction structure were the enrichment regulation.