Study Of The Reservoir Characteristic Of N₂¹-N₂² In Nanbaxian Oil-gas Fields In Qaidam Basin

Nanbaxian structure located Faulted Block Belt in Northern Margin of Tsaidam Basin in Qinghai Province is a three-stage structure of the Mahai-Dahonggou uplift subregion.Nanbaxian oilfield is the main oil and gas field in northern Tsaidam Basin.Distribution and heterogeneity of reservoir has been plagued development well and injection well deployment and remaining oil prediction.According to this problem,Reservoir petrological characteristics,depositional microfacies,four-property relationship,reservoir heterogeneity and genetic mechanism are studied using the data of core,drilling,logging.Lake facies and delta facies developed in the Pliocene Series is mainly two types of sedimentary facies,and it's the microfacies is various.By researching the data of core and drilling and well logging,it was considered that the sedimentary facies,such as delta and lake facies wrer developed in Nanbaxian Area,controlled by the source from the North east and north east.The two facies could be subdivided into distributary channel,natural barrier,inter distributary bay,crevasse splay,underwater distributary channel,underwater inter distributary area,channel mouth bar,distal bar sand sheet,delta front,predelta mud,beach,bar and mud flat microfacies.Delta front subfacies distributed mainly in the north east and south east direction in the south of the Nanbaxian oil fields.Coastal and shallow lake facies distributed mainly in central and western the Nanbaxian oil field.South of the Nanbaxian Oil-gas Field reservoir rock types are divided into mainly fine sand and silt With various pore types.Sandstone grain size is commonly0.05-0.25 mm.The structure maturity and Composition maturity is relatively low.Reservoir pore include mainly primary intergranular pore,residual intergranular pore and intragranular solution pores,intergranular dissolved pore and intracrystal solution pores,intergranular dissolved pore type;fracture include clastic particles of compressive fracture and calcite crystal cleavage lines.The reservoir type is controlled by types of sandstone bodies in the Nanbaxian oilfield.The reservoir is mainly divided into three types of reservoir: ?class reservoir are mainly delta-fine sandstone reservoir from branch channel,with good physical properties,and it's the best porosity is greater than 20%,permeability is greater than 100×10-3?m2;? class reservoir is coarse sandstone and conglomeratic sandstone and conglomeratic sandstone from the braided channel sand body and parts shallow lake bar,with Medium property physical properties,and the porosity is10%-20%,permeability is less than 10×10-3?m2-100×10-3?m2;? reservoir include conglomerate,sandstone and argillaceous siltstone from beach bar sand body of shallow lake,with poor physical property.porosity is less than 10%,and permeability is less than 10×10-3?m2.Distribution of reservoir performance strong heterogeneity in the Nanbaxian oilfield.Reservoir internal anisotropic is strong from upper and lower Youshashan formation.strong heterogeneity occupies first place,weak heterogeneity comes second and proportion of medium heterogeneity occupies least for Intraformational heterogeneity.Interlayer heterogeneity is medium-strong heterogeneity.Plane distribution Heterogeneity of sand body of Small layer is medium.Small layers sand body is mainly a connectivity medium-good belt,wide band,and local show connecting sheet distribution.