The Deposition Architecture And Relation With Gas-oil Of The Depressional Lacus Delta Front Of Yanchang Formation In Ordos Basin For Example:Oil Group Chang-3 In Longdong Region

Ordos Basin is a large Mesozoic basin, which has rich energy resources and keeps completely Mesozoic strata in China. Yanchang Formation is one of important oil-bearing Formation. In the basin Yanchang Formation is a lithologic encirclement deposit, and is strictly controlled by sedimentary facies. This paper studies the depositional architecture of depressional lacus delta front and its relation with oil and gas through three aspects: sedimentary, reservoir, oil accumulation of Chang-3 period, Yanchang Formation in LongDong region.Yanchang Lacus is a depressional lake which has slightly dipping east rivage and high dipping west rivage. At the two rivages upgrowth two different kinds of delta depositional system:east nvage is mild slope delta and west is steep slope delta.On the basis of an intensive study and depiction of sedimentary microfacies of delta front, we make great advance. Specially discuss two main niicrofacies of oil storage: submerged distributary channels and river mouth bars. According to the analysis, classify precept and discriminating symbol are built. For example, submerged distributary channels are described fourteen sorts at four arrangements and river mouth bars are described nine sorts at three arrangements.IvThe formation of the five kinds of sandbodies is proposed according to the strength of the currents in the distributary channels and the depth of water in the lake. At the same time deduce the mechanism of formation of recombination bars microfacies. On the one hand, with the increase of energy of river, it may traverse and corrode river mouth bars, forming recombination bars of distributary channels corroding river mouth bars. On the other hand river mouth bars would deposit first, then accepting sedimentary of distributary channels, as there is a center of subsidence.On the basis of an analysis of different kinds of reservoir抯 petrologic feature ,porosity,rate of percolation, we can conclude that anisotropy controlled by depositional facies. The porositymainly distributes in the middle of 10.02-12.97%. The rate of2percolation is average 2.45 X i0~ 1-~ m Its physical property isthe best in comparison to other kinds of sandbodies.This paper summarizes the forming model of petroleum deposit which is deep-water facies, river over bar, sandbodies without root and small anticlise (nose surrectic structure) after studies the depositional microfacies architecture and the reservoir抯 anisotropy of delta front.