South Mud Bend Oilfield Extend Sedimentary Facies And Reservoir Characteristics

AbstractOil-gas concentration of Yanchang group of Upper Triassic in Nanniwan exploration area is mainly controlled by good facis,which is alike to the other regions of North Shannxi,belong to the typical lithologic deposit of lacking structural trap．So blocking out sedimentary microfacies and studying distribution of sedimentary facies are important content in this study area．In the basis of the facies markers and facies analysis of principle, there are mainly river,delta and lake depositional sysytems in Upper Triassic of Nanniwan field,in which all kinds of difference sedimentary subfacies and sedimentary microfacies are distinguished, such as meandering river,delta plain,delta front,submerged distributary river course,frontal sheet sand and so on．The prominent feature of the Nan Niwan delta is that submerged distributary river course sandbodies are framework sandbodies,river mouth bar is undeveloped and vertical sequence is incomplete．In time and space all kinds of facies have regular evolution trend in study area．After the lake positively movement largely in Chang 7 medium period,and evolving in Chang 6 period,Chang 4+5 period,there is a fluvial-lacustrine sediment system because of filling of deposition from river．The delta in Chang 6 reservoir is very developed,the lake—water withdraw from Northeast to Southwest．In Chang 4+5 period,delta plain is formed in large range and marsh plain is developed．In the reservoir,the maturity of component is low,but the maturity of structure is high．According to the characteristic of the coventional physical property and the pore structure,the pore throat in this region is separated to three kinds,they are middle pore low permeability,low pore extra low permeability and no-permeability respectively．In study area,the low pore extra low permeability is the most important pore category．The research shows that the source-reservoir-seal assemblage and oil-gas concentration are controlled by microfacies．The reservoir sandbodies can be blocked into channel bar of meandering stream,submerged distributary channel sandbodies,river mouth bar and sheet sand of delta front,distributary channel of delta plain,etc．The physical properties of channel bar of meandering stream,submerged distributary channel sandbodies and river mouth bar of delta front are better than the other．In this region,the main reservoir sandbodies are submerged diatributary channel sandbodies．...