Types Of Shale Lithofacies And Its Geochemical Characteristics Of Upper Cretaceous In SK-? Borehole

There are a large number of mudstones from the first member of Qingshankou formation to the second member of Nenjiang formation in the section of SK-? borehole.The lithofacies types and the organic geochemical characteristics vary greatly.The predecessors have described the lithofacies and analyzed the organic geochemical characteristics detailedly.But there is no systematic analysis and summary about the organic geochemical differences and the reasons forming different lithofacies.In addition,it is hoped to try to identify different types of lithofacies using logging characteristics.In this paper,core,logging,and geochemical analysis data are used to classify the shale lithofacies from the first member of Qingshankou Formation to the second member of Nenjiang Formation.Using the color,TOC and sedimentary structure of shale,the Upper Cretaceous shale facies of the SK-I borehole was divided into four major categories: two dark-colored lithofacies types,two light-colored lithofacies types,and other special lithologies;By analyzing the color,sedimentary structure,TOC and logging characteristics of various types of lithofacies,the upper Cretaceous sedimentary facies of the SK-I borehole was determined.Based on the classification of shale types,the geochemical characteristics are analyzed.Different types of mudstone lithofacies have different organic matter abundances,types,and other geochemical characteristics.Black and gray black horizontal bedding mudstones are rich in organic matter abundance.The type of organic matter is dominated by type I and type II.The paleo-productivity is high and it is very favorable for the formation of high abundance source rocks.Light-colored shale facies have poor organic matter abundance,and organic matter is dominated by type II or type III.Large variations in organic matter types generally fail to form high-abundance source rocks.The characteristics of the cyclic evolution of different types of mudstone lithofacies are related to the cyclical changes of paleoclimate.Different types of mudstone facies developed different climatic backgrounds.It is easy to develop black horizontal bedding shale facies under the warm,wet,deep water depth sedimentary background;The sedimentary background with arid climate and shallow depth of water is prone to development of purple-red organic-matrix massive structural mudstone facies.