Deep Water Sedimentary And Reservoir Characteristics In Yanchang Formation Of Yaoqu Outcrop Zone In Ordos Basin

Ordos basin is a large depression basin in China and the lake basin expanded during the sedimentary period of the Chang7 oil formation of Triassie Yanchang Formation in upper triassic.The research area developed a large amount of gravity flow deposition.In the southern part of the basin,the layer of Chang6 &7 formations is good area of observation,which provides abundant information for the fine sedimentary dissection and reservoir characteristics.In this paper,the authors studied the deep-water gravity flow sedimentation of Chang6&7 oil formation in Yaoqu area of ordos basin.In the field,the data such as the field test profile and 167 samples of rock flake,particle size experiment,scanning electron microscope,pore infiltration experiment and so on were used.Based on the structure of the sediments and the difference of tectonic characteristics of the region has carried out detailed dissection in sedimentary characteristics,process and configuration.The results show that:(1)The sandstones are dominantly made up by bad-sorted and bad-rounded fine sandstone-siltstone,and they are mainly lithic arkosic sandstone and feldspathic polylitharenite.(2)There are 14 types of lithofacies and 9 lithofacies combination.The cumulative thickness of fine sandstone facies is the biggest,followed by horizontal bedding mudstone facies,mixed source boulder clay block sandstone facies,endogenous boulder clay block sandstone facies,the massive net mudstone facies,graded bedding fine siltstone facies.(3)The process of sedimentation of the research layer is analyzed on the basis of the classification of lithofacies and the lithofacies combination.Identify 5 sedimentary processes: turbid flow,sandy clastic flow,slump,normal deep water deposition,tractive current.The turbidite deposition are characterized by the Bouma sequence,and the sandy clastic flow deposits are mainly composed of massive block sandstone,and floating gravel and mudstone crumbs areseen in the bottom and top positions.The collapse deposition is made by typical sand mud mixed,and the sandstone bands are crumpled and deformed,and liquefied sandstone veins,convolute bedding,slippage breccia and ball-and-pillow structure.The tractive current deposition in the research area is mainly based on the trough cross-bedding and the directional imbricated boulder clay.The normal sedimentation of deep water is characterized by deep water horizontal bedding shale.(4)Combined with sedimentary morphology,identify four sedimentation units: the deep-water channel,overbank,lobe,slumping block deposits.The deep-water channel of the study area is dominated by sediment-erosion transition channel.Through the analysis of the fine scale configuration,there are four types of deep-water channel superimposed styles:vertical superposition type,lateral splicing type,side swing superposition,oblique column superposition.Combined with the results of sedimentary process analysis,set up the sedimentary model of slump-flood mixed gravity flow deposits.(5)The characteristics of the reservoir in the study area are analyzed in detail.Primary pore pore width is 5-200?m.There are granular intergranular pores,intramolecular pores.The latter is irregular in shape,with pores at the edge of a bay and later filled with clay or carbonate minerals.Cross bedding sandstone facies reservoir performance is best in the lithofacies types,the waterway vertical stacking patterns of reservoir quality in the sedimentary units is best.