The Study On Sedimentary Facies And Reservoir Characteristics Of Yan7 Oil Group Of Jurassic Yan'an Formation In YanWu Area,Ordos Basin

Ordos Basin is located in the central and western regions of China,which is the second largest sedimentary basin in China.It is a multiple cycle composite basin with abundant oil and gas resources.This study area is Yanwu area of Ordos Basin.The area is located in the southwest of Ordos Basin,which is located at the southern of the Yishan slope in Tianhuan depression.The overall shape of the structure is high in the east and west and low in the north and the south.Its structure is simple.Some areas develop some nearly east-west low amplitude nose structures and dome structures and faults don't develop.There is no large uplift in the basement and obvious features of inherited development.In recent years,the exploration and development of the southwestern regions of Ordos Basin shows that the Jurassic Yanan formation in this area has considerable oil and gas resources.Now based on the study of the Jurassic stopes wellblock well point and understanding,for overall arms drill region is relatively weak,with arms drill valley stratigraphic classification and correlation on both sides need to carry on the fine alignment,yanan group change laws of sand body on the transverse longitudinal also need detailed characterization,for the parameters of the reservoir and the reservoir characteristic research remains to be further deepened.Supply pressures are increasing with the surge in demand for oil and gas,but as the exploration progresses,the exploration becomes more difficult.This paper comprehensive studies the arms drill area formation of Jurassic Yan'an group Yan 7 reservoir distribution characteristics?sedimentary microfacies types and sand body,and the distribution of reservoir characteristics,for further study on the late work area as main control factors and analysis of oil and gas enrichment regularity to build a solid theory foundation.This paper had Ordos basin Valley Branch Yanwu Jurassic Yanan group Yan 7 oil-bearing formation group as the research object.It systematically used theoretical basis of Geology and was based on core data,logging data and some drilling data.It had comprehensive research of Yan 7 oil-bearing formation through the analytical tests of slice,particle size,scanning electron microscope and micro element.It had fine stratigraphic division and correlation of Yan 7 oil-bearing formation through the theories of marker layer method,formation thickness method and sedimentary cycle method.It detailedly analyzed the regularity of stratigraphic distribution relationship,formation thickness and rock-electricity relation.In the study,through the stratigraphic study it established paleogeomorphological model of the Branch Valley Yanwu Pre Jurassic.It studied the depositional system division,sedimentary microfacies identification,sand body plane distribution and reservoir characteristics on the basis of core observation,logging data and analysis of test data.In this study,470 wells in the study area were divided and contrasted.It established 20 stratigraphic correlation sections which included 5 horizontal sources and 6 perpendicular sources.The contrastive results showed that the continuity of the study area is good,the thickness of the formation is stable,and the development of the coal seam in the top of the Yan 7 oil-bearing formation of is stable as same as the bottom of the coal seam which developed 1-2 sets of coal seam with about 10 cm thickness.The Yan 7 oil-bearing formation can divided into Yan 71 whose thickness was 15 to 25 cm and 72 whose thickness was 20 to 30 cm according to the characteristics of cycle and strata thickness.Yan 7 oil-bearing formation in the study area is Fluvial delta depositional system.This paper is more inclined to braided river delta sedimentary system.It was mainly delta plain which developed distributary channel,interfluve depression,natural levee and marsh established the depositional stage sedimentary model of Yan 7 oil-bearing formation.The depositional stage of Yan 7 oil-bearing formation was main the sand deposit in distributary channel and sand bodies had a banding distribution along the northwest-northwest direction.Sand bodies' lithology is coarse and mainly is fine sandstone and coarse-mid sandstone which developed trough cross-bedding,plate cross bedding and massive bedding.Research showed that Yan 7 oil-bearing formation in the branch valley of Yanwu Yan 7 oil-bearing formation was low-mid permeability reservoir.The pore structure mainly consisted of coarse-mid and the properties of matter was fine.Lithology was mainly composed of lithic arkoses and then the lithic feldspathic sandstones.Total quartz accounted for 62.59%,feldspar accounted for 19.66% and detritus accounted for 17.75%.Average porosity of Yan 7 oil-bearing formation was 14.55% and average permeability was 23.12×10-3?m2.The properties of matter was the change trend of decreasing from top to bottom.