The Study On Sedimentary Mircofacies Of Chang 8 Oil Formation In Jiuxian-Jiaoping,Southern Of Ordos Basin

Chang 8 oil-bearing formation in JiuXian-JiaoPing area,located in the southern part of Ordos Basin,is rich in abundant oil resources.but the contradiction of deep exploration degree and low geological study is increasingly obvious.Sedimentary microfacies and sand body distribution is still controversial.The further exploration of oil and gas becomes difficult.Based on sedimentary principle and integrated use of the theory and methods of sedmentary petrology,petroleum geology,logging geology,through a comprehensive analysis of the outcrop,drill core data and logging data,the paper studies the source direction,sedimentary facies types and distribution of sedimentary facies of Chang-8 oil formation of the Triassic Yanchang Formation of Jiuxian-JiaoPing area of Ordos Basin.To classification and correlate the stratum,through the way of flag layer control and cycle contrast,combined with the thickness principle,we divide Chang-8 oil formation into Chang81?Chang82 in study area.The top layer structure is presented the characteristics of high-southeast and low-northwest uniclinal structure features,partially developing nose-like apophysis.Through the study of paleocurrent direction,light and heavy minerals,rock debris analysis,as well as ancient land distribution feature,we think the study area mainly affected by the northeast and the southwest provenance,and locally influenced by the south provenance.We speculate that northeast provenance was from archaeozoic metamorphite of Yinshan Mountains and Daqingshan Mountains,southwest provenance was from Longxi old land and south provenance was from Qinling orogenic belt.According to core description,outcrop,combining with the rock type,structure characteristic and sedimentary structure and old biology feature etc,we identified that Chang-8developed delta-lacustrine sedimentary systems in study area.and the delta belongs to shallow water delta.To the further study,facies can be divided into two types of sub-facies including delta-front and former delta-shallow lake,which can be further divided into six categories of micro-phase:underwater distributary channel,estuary dam,distal bar,interdistributary bay,distributary channel flank,predelta mud.Through single well facies analysis and connecting-well sections comparison,we draw the distribution fig of sedimentary facies and sand body in different period.On the chang8 layers of horizontal,the sand body of delta frontunderwater distributary channel and far bar present strip shape and lens shape,interspersed with between distributary bay,and surrounded by shallow lake subfacies;On the plane,delta front facies and shallow lake subfacies is the main sedimentary facies of chang8.There are multiple underwater distributary channel in the study area,convergence,divarication,it is developed underwater distributary channel flank.Between distributary bay presents irregular shape around it.Shallow lake mainly in the northeast and central in the study area.Sedimentary microfacies control the distribution regularity of sand body,The thickness and continuity of the sand body of chang81 better than chang82.