Application Of Elemental Logging In The Study Of Sedimentary Facies And Sequence Stratigraphy Of Carbonate Rocks

The Yijianfang Formation and the upper Yingshan Formation in the Shunnan area are mostly carbonate reservoir development sections,and conventional tests of several wells have high-yield industrial gas flow.However,the carbonate rock has single composition and complex structure,and controlled by many factors in the process of sedimentary evolution.Using traditional data,it is difficult to identify and predict,so the current study of the sequence stratigraphy and sedimentary facies of the target interval in the study area is not refined and quantified enough.The sedimentation-diagenesis process of carbonate rocks is controlled by chemical action and is closely related to the changes of various elemental content.Therefore,exploring element logging data in study of sedimentation-sequence of the study area will help to further understand the sedimentary facies distribution of high-energy facies in the Yijianfang Formation and upper Yingshan Formation.Guiding by the theory of sedimentary geochemistry,combined with the traditional thin sections and well logging data,this paper discusses the method and process of dividing carbonate sedimentary sequence by using element logging data,and carries out sequence division and sedimentary facies analysis.On the basis of a large number of literature research,cluster analysis method is combined with regional sedimentary background to analyze the geological environment change factors controlled by element content change.Fifteen commonly used elements or ratio parameters are divided into three categories,which correspond to the formation of carbonate rocks,paleoclimate,paleo-water depth,organic matter content and redox conditions of sedimentary environment.Summarize the conditions to selected characteristic parameters and select five characteristic parameters according to the actual conditions in Shunnan area: Dis,Ca,V/(V+Ni),Mg/Sr and Mn/Fe.The characteristic curves is extracted by Morlet wavelet analysis and EEMD(Ensemble Empirical Mode Decomposition),the target layer is divided into eight complete fourth-order cycles.The upper Yingshang Formation identifies five complete fourth-order cycles and the Yijianfang Formation identifies three complete fourth-order cycles.Based on the thin section data of cuttings,lithologic assemblage characteristics,and combined with the sedimentary background of the study area,three subfacies are divided.There is a good correspondence between the low-energy intertidal subfacies and the flooding interface identified by the fourth-order cycles,while the high-energy sedimentary environment are well developed in the early stage of sea level rise and decline.Therefore,the geochemical information contained in the cuttings logging data can really reflect the changes of sedimentary environment in the sedimentary area,and the method of multivariate analysis has a good effect on finding characteristic elements.On this basis,it has guiding significance for further division of stratigraphic sequence and sedimentary facies.However,cuttings logging data also have its limitations.How to further subdivide subfacies and microfacies with small differences in sedimentary environment remains to be studied.