Logging Evaluation Of Sifangtai Formation In The South Of Daqing Placanticline,Songliao Basin

The area studied in this paper is in a certain area in the south of Daqing Placanticline in Songliao Basin,and an industrial-grade uranium deposit has been found in the Sifangtai formation in the study area.This paper focuses on the evaluation of in-situ leachable sandstone-type uranium deposits by using logging data,supplemented by logging,geological and core data,to solve a series of problems in the study area,such as stratigraphic framework,sedimentary facies distribution,reservoir physical properties and so on.After collecting and collating the data,this work first carries on the stratigraphic division and correlation,and uses the marker layer correlation method to identify a mudstone marker layer in the study area.Under the constraint of the marker layer,the strata are divided according to the shape of the logging curve,the layer interface of the Sifangtai formation is identified,and the Sifangtai formation is divided into the first member of the Sifangtai formation and the second member of the Sifangtai formation.The top structure of the first and second member of Sifangtai formation is high in the east and low in the west,and the height difference of depth is about 100 m.It is estimated that the trend of the interface is relatively gentle,and the dip angle is 1°-2°.The thickness range of the second section of Sifangtai formation is 27.81-39.05 m,and that of the first section of Sifangtai formation is 33.14-45.18 m.The sandstone of the second member of Sifangtai formation is mainly distributed in the north,northeast and southwest of the study area,and the lithology in the study area is mainly mudstone;the sandstone of the first member of Sifangtai formation is widely distributed in the study area,and the sandstone is relatively thick.the lithology in the study area is mainly sandstone.On the basis of understanding the regional structural background of the study area and the distribution of sedimentary facies in the adjacent area,the core and logging curves are used to study the sedimentary facies in this area.By analyzing the logging response characteristics of different lithology,selecting the combination of natural gamma and resistivity curves in the study area,using the principle and method of logging facies to analyze the curve morphological characteristics of the sedimentary sequence,combined with the sedimentary background of the study area,the sedimentary facies of Sifangtai formation are analyzed and identified,and it is considered that meandering river facies are mainly developed in the study area.Then,based on the sedimentary environment of fluvial facies,the fluvial facies is subdivided into three subfacies: floodplain,channel margin and channel.The natural gamma curve is a combination of bell type and toothed box type,with high resistivity and large thickness of strata deposition,which reflects stable hydrodynamic or provenance supply,and is comprehensively judged to be channel deposition.The natural gamma curve is a combination of finger type and micro-tooth type,and the thickness of each layer is not large,the sand-mudstone interlayer is frequent,and the resistivity value is not high,which reflects the unstable provenance and can also be understood as the sedimentary phenomenon caused by the channel change.It can be comprehensively judged as the deposition on the edge of the river.The natural gamma value is high,the curve is very flat,the resistivity value is also very high and flat,and the lithology of the deposit is mudstone,which is comprehensively judged to be floodplain deposit.When using the logging curve to obtain the distribution of porosity and permeability in the study area,the conventional model is used to calculate the porosity and permeability of the non-uranium ore section,and when the layer contains uranium ore,the method of increasing natural gamma correction density and other methods of reconstructing natural gamma ray from radioactivity-free curves are used to achieve the purpose of accurately obtaining physical parameters.The results show that the lithology of the second member of Sifangtai formation is mainly mudstone,with less sandstone,the range of porosity is about 6%-25%,and the median is 17%.The porosity distribution of the first section of Sifangtai formation is wide,the range of porosity is about 6%-28%,and the median is 20%.Similarly,for the fitting of permeability model,the method step is similar to that of porosity model,the distribution law of permeability is consistent with that of sandstone porosity,and the range of permeability is between 0.01-104 mD.Finally,the above work is sorted out,on the platform of geological modeling software Petrel2015,using variation function analysis technology and random modeling algorithm,structural modeling,facies modeling and attribute(porosity,permeability)modeling are completed,and the characteristics of underground geological bodies are analyzed according to the existing understanding of the study area.In order to verify the model,the comparative analysis of physical properties before and after modeling and the analysis of lithofacies profile are carried out.The results show that the established model is consistent with the understanding of the study area.