Characterization And Modeling Solutions For Complex Reservoir Of The 3rd Member Of Liushagang Formation In WZ11-1 Oil Field

Most of oilfields in China have recently entered into the middle-later period of development,where reservoir complexity and serious injection-production contradiction were common,the traditional reservoir heterogeneity study has transferred to reservoir architecture.WZ11-1 oil field was located in the northwest part of Weixinan sag,Beibuwan Basin.The 3rd member of Eocene Liushagang Formation in Paleogene was the major production layer in this block.The 3rd member of Liushagang Formation was confirmed as continental complex reservoir deposited during the rifting period of rift basin,which was characterized by multi types of depositional types,complex lithologies;unclear genesis mechanism of the thin interbeds in the upper part and thick layers with box-shape in the lower part,scales of sandbodies,superposition relationship and connectivity;rapid decline of production in thin layers and poor results of water injection in thick layers with box-shape,leading poor performance in development.Therefore,based on cores,well logging and seismic data,guided by the theory of reservoir sedimentology and sequence stratigraphy,high resolution sequence stratigraphic framework has been established and types of sedimentary micro-faces have been confirmed in this paper to figure out the distribution rules and evolution characteristics of reservoirs by core description,genesis sandbodies correlation constrained by facies,and 3D characterization.Architectural characterization of reservoir sandbodies and superposition models of gneiss sandbodies has been summarized.Also,the major controlling factors that affected the architectural characterization of reservoir sandbodies have been analyzed to realize the description for architecture unit of thick layers with box-shape and gain quantization for scales of sandbody with different genesis,forming solution of geological modeling for complex reservoir.Major conclusions and innovation of this paper were listed as follows:1.High resolution sequence stratigraphic framework has been established.The target horizons of the study area have been divided into one 3rd order sequence,four 4th order sequences and nine 5th order sequences,where the 3 rd order sequence was bounded by unconformity and the 4th order sequence and the 5th order sequence was bounded by transgressive(lacustrine transgressive)surfaces.Two types of sedimentary subfacies(meandering river delta front and braided river delta front)were identified within the isochronous stratigraphic framework,of which,meandering river delta front developed in the upper of the third member of Liushagang Formation,while braided river delta front developed in the lower of the 3rd member of Liushagang Formation.2.Distribution rules and evolution characteristics of reservoirs in the 3rd member of Liushagang Formation have been confirmed.Provenance for the 3rd member of Liushagang Formation was from the northwest direction.From bottom to top,LST,TST and HST were developed successively.Thick layer in the LST was the braided river delta inner front formed by progradation(regression).Interbeds in TST were braided river outer front formed by retrogradation(transgression).Interbeds in LST were meandering river delta front formed by progradation(regression).3.Based on genetic sandbodies correlation among wells constrained by facies,three sandbody structure models and 11 genetic sandbody superposition models(3 types and 6 subtypes)have been summarized,realizing the characterization of architectural unit in thick layer with box-shape.Thick layers in LST were multi-layer,where the genetic sandbodies were dominated by dissected superposition,with good connectivity both in lateral and vertical.Interbeds in TST were single-layers,the genetic sandbodies were dominated by dissected superposition and butt joint superposition,where the lateral connectivity was better than vertical connectivity.Thin layers near the MFS were isolated,genetic sandbodies were dominated by isolated-type in lateral and vertical.Interbeds in HST were single-layer,the genesis sandbodies were dominated by dissected superposition and butt joint superposition.According to analysis,it can be confirmed that MFS was the major factor that controlled the sandbody structure of reservoir and superposition relation of genetic sandbodies.4.Scales of sandbodies with different genesis have been quantified,where average width of underwater braided channel in braided river delta front was 350m,average width-thick ratio was 1:60;average width of river month bar was 350m,average width-thick ratio was 1:70.Average width of underwater distributary channel in meandering river delta front was 300m,average width-thick ratio was 1:90;average width of river month bar was 290m and average width-thick ratio was 1:80.5.Solution of 3D geological modeling for complex reservoir has been formed.For the thin layers,which were characterized by thin and large quantity,micro-faces model can be established by multiple-point geostatistics first.Then,parameter model for thin layers can be built constrained by facies.For thick layers with box-shape,lithofacies model can be built constrained by architectural and planes on the basis of reservoir architecture analysis.Then,parameter model of reservoir architecture can be established under the constraining of facies.