Study On The Reservoir Characteristics Of Braided River In The Yan'an Formation Of The Middle Jurassic, Dingbian Area

The Dingbian area is located in the western part of the Yishan Slope,Ordos Basin.It is an important oil-producing area and has received extensive attention.At present,the research level is difficult to meet the needs of the next exploration and development.For the problem of the Dingbian area,this paper is guided by petroleum geology,logging geology,sedimentology and sedimentary basin analysis,based on previous research results and surrounding outcrops.Observation,drilling core description,oil test and production data,combined with particle size analysis,cast thin section,scanning electron microscopy and mercury intrusion test,the stratigraphic division,sand body distribution characteristics,The petrology,structure,heterogeneity,sensitivity and wettability are deeply analyzed of the Yan10 Formation.On this basis,the reservoir is comprehensively evaluated and the following understandings are obtained:?1?According to the unique marking layer of the Yan 10 Formation in the Dingbian area,Ordos Basin,combined with the core of the drilling,the characteristics of the logging curve and the characteristics of some sedimentary cycles,the Yan 10 Formation is subdivided into Yan 10³,Yan 10²and Yan 10¹,each small Formation in structural form similar,with succession,the terrain is high in the east and low in the west,the development of a number of near east-west low-middle structure nasal.?2?The Yan 10 formation is mainly composed of braided river sediments.The sedimentary microfacies are mainly river sand dams and floodplains.The micro-facies type is mainly the interaction of river sand dams and floodplains,and the sand dams are deposited.Mainly,the lithological section is characterized by less sand and more mud,thick sand layers and coarse particles.?3?The rock types of the Yan 10 formation are mainly feldspar sandstone,lithic feldspar sandstone and feldspar lithic sandstone.The sandstone grain size is mainly medium-coarse grain,and the roundness is mainly round.The pore combination is mainly intergranular pores.The average porosity of the Yan 10 oil layer group is 15.15%,the average permeability is42.60×10^-3?m²,which belongs to the mesoporous low permeability reservoir.The diagenesis type of the Yan 10 formation is mainly pressure,cementation and dissolution,and the heterogeneity of the 10 formation is moderate.?4?According to the classification criteria of reservoirs in northern Shaanxi,the Yan 10formation is divided into effective reservoirs Ib and IIa,non-effective reservoirs IIb and IIIa,of which Ib reservoirs and The reservoirs of type IIa are mainly developed in the main part of the river,and the sand bodies are relatively developed.The reservoirs of type IIb and IIIa are developed at the edge of the river.The analysis proves that the group of Yan 10 oil layer is mainly Ib and IIa.Low permeability layer.