Development Mechanism Of Reservoirs Under Sequence Stratigraphic Architecture Of Late Triassic Yanchang Formation In Jiyuan Area,Ordos Basin

Ordos Basin,which is rich in natural resource such as coal,petroleum,natural gas,etc,is a polycyclic superimposed craton basin.Triassic Yanchang Formation is the first formation in which petroleum and natural gas were found in Ordos Basin and thus it is the main target strata in exploration and development for many years.Along with the exploration and development of the Ordos basin for decades,the oilfields discovered and developed indicate that the upper Triassic oil and gas reservoirs are mainly characterized by the lithologic stratigraphic oil-gas reservoirs.The lithologic stratigraphic oil-gas reservoir controlled by lithofacies and strata has become the most promising new field for hydrocarbon exploration in the formation of the Late Triassic in the Ordos Basin.Jiyuan Oilfield,located in the northwest of the Ordos Basin,is the largest oilfield for the scale of reserve and production in Mesozoic petroleum exploration and development of Ordos Basin.Recently,Xin'anbian oilfield,the first hundred million tons of large dense oilfield in China,has been found in Jiyuan area,which fully indicate that the great potential of oil and gas resources in Jiyuan area of Ordos Basin.With the increasing exploration efforts in Jiyuan area,the more abundant information can be used to research.Therefore,it is necessary to study the region of the sequence stratigraphic framework,sedimentary system,sand-body continuity and distribution characteristics,and favorable areas.Based on the theory of high-resolution sequence stratigraphy,through analysis and comparison of the drilling,logging and other data in Jiyuan area,the isochronous stratigraphic framework of Yanchang Formation is established,and the Yanchang Formation in the study area is overall divided into 4 long-term base level cycles(LSC1-LSC4)and 14 medium-term base level cycles(MSC1-MSC14).LSC1,the long-term base level cycle,can be further divided into 2medium-term base level cycles(MSC1-MSC2),LSC2 into 3 medium-term base level cycles(MSC3-MSC5),LSC3 into 4 medium-term base level cycles(MSC6-MSC9)and LSC4 into 5medium-term base level cycles(MSC10-MSC14).By comparative analysis of the core and the logging data of the study area,the logging facies identification templates are established and used to identify the different types of sedimentary facies.On the basis of the above work,with the guidance of sedimentary petrology,the sedimentary micro-facies cross-sections and the sedimentary facies plans under the up or down half-cycle of the medium-term base level cycles from MSC4 to MSC10 are compiled,and the sand bodies distributions of Yanchang Formation are described in the study area,in which delta-lake sedimentary system developed,and the distributary channel sand body is the main reservoir sand body.Based on the study of sequence and sedimentary facies,the reservoir physical properties of the key layers of the medium-term base level cycles from MSC6 to MSC7 in the study area are analyzed,and the contour map of the porosity,the permeability and the sandstone thickness under the up or down half-cycle of the medium-term base level cycles from MSC6 to MSC7 are drawn.On the basis of the contour map of the porosity,the permeability and the sandstone thickness,together with the sedimentary facies plan,8 favorable areas of the key layers in the study area are identified with 7 Type?and 1 Type?,and the exploration and development in the future indicated as well.