The Reservoir Description Of The Cretaceous Oil Sands In Fengcheng Area,Junggar Basin

The oil sands deposit of Fengcheng area locates in the northwestern margin of Junggar Basin,and it is the most abundant region of oil sands deposits in China.At present,this area is in early stages of development,and the understanding of the depositional feature,reservoir characteristics and oil sands distribution of Cretaceous Qingshuihe formation is insufficient.By the comprehensive study of geological characteristics,we can make sure the oil rich layer and block to provide a basis for the next exploitation.Firstly,the signs of division are found,through integrating analysis of cores,well logging,drilling,test data,etc.Then the Cretaceous Qingshuihe formation is classified and correlated,with the guidance of multi-disciplinary theory of Sedimentary Petrography,Reservoir Geology,and Reservoir Assessment Technology.On the basis of classification the sedimentary microfacies are studied,through analyzing coring wells and considering the distribution characteristics of sandstone,the sedimentary microfacies of target stratum are divided into four types: underwater distributary channel,underwater inter-distributary deposit,braided channel and channel bar.With the data of well log interpretation,thin slice,scanning electron microscope and mercury injection capillary,the microscopic and macroscopic features of reservoir are studied,and the microscopic study includes the type of reservoir space and pore throat structure characteristics,etc.Then do research on the macroscopic heterogeneity from the aspects of in-layer,interlayer and plane.The research shows that the heterogeneity of in-layer is gradually weak,the interlayer and plane are gradually strong from K1q23,K1q22 to K1q21 formation.The reservoir has been divided into four categories by a method of classification called ?weight evaluation?.Among the categories,the first grade and second grade are the most favorable reservoirs in this area,and mainly distributed in No.1 oil sands area.Usually these kinds of reservoir are with high porosity and high permeability,and the average porosity is higher than 31%,and the average permeability is 1294.7×10-3?m2.The crude oil analysis shows that the main groups of crude oil from oil sands are nonhydrocarbon and asphalt,and small amounts of saturated hydrocarbon and aromatic hydrocarbon.This phenomenon indicates that the crude oil has suffered from severe biodegradation.On the basis of the above researches,the oil sands concentration pattern has been summarized.The oil sands distribution in this area is affected by the following factors: sedimentary facies,reservoir heterogeneity,the distribution of faults and unconformity and burial depth.In the plane,oil layers are distributed mainly near the fault blocks of FS73,FZ007,Z1 and Z32.In the longitudinal direction,the oil-bearing area in K1q23 is the largest,and it is the main formation of oil sands accumulation.Finally under the constraint of sedimentary microfacies,the 3D geological model for target formation has been established by stochastic modeling technique.Respectively to projections on spatial distribution of reservoir properties(porosity,permeability and oil saturation),and the results fit well with the actual development situation in the study area.