Application Of Geochemical Logging In Paleoenvironment Analysis Of Well SK-2

The abundance and combination of elements in rocks can directly reflect the enrichment and dispersion of elements,which is the main basis for displaying a lot of geological information.Logging data is widely used in petroleum exploration,sedimentary stratigraphy and other fields because of its strong continuity,high vertical resolution and rich information.Unlike conventional logging data,geochemical logging mainly measures the content of some elements and minerals in the formation.A large number of high-quality data were collected by geochemical logging method in well SK-2,which provides basic data and scientific basis for the analysis of sedimentary environment and a series of geochemical problems in Songliao Basin,and has reference significance for solving paleoenvironment and paleoclimate problems based on geochemical logging method in the future.Based on the geochemical logging data of well SK-2 and a large number of literatures at home and abroad,this paper systematically studies the paleoenvironmental changes of well SK-2 during the Cretaceous sedimentary period.Firstly,based on core logging data and geochemical logging data,the evolution process of Cretaceous sedimentary facies in well SK-2 and its corresponding geochemical logging response characteristics are clarified;Secondly,the element mineral logging data sensitive to environmental changes are selected,and the sedimentary facies of well SK-2 are divided by cross plot;At the same time,by calculating the characteristic parameters of the sedimentary environment,combined with the paleogeological events occurred in the Cretaceous sedimentary period of well SK-2,the Cretaceous paleoenvironmental evolution of well SK-2 was analyzed from four aspects:redox environment,relative paleowater depth,paleosalinity,paleoclimate and humidity.The results show that the meandering fluvial facies and lacustrine facies can be well divided by using the cross plot of the total contents of Ca,Fe,S and Si;At the same time,the braided river and fan delta facies of well SK-2 can be divided by using the content of Al,Ca and Fe as well as the cross plot with Na and S.The calculation and analysis of pyrite content,Th/U,U_xsand other parameters show that the evolution process of Cretaceous redox in well SK-2 is"weak reduction weak reduction weak oxidation weak reduction weak reduction weak reduction",and the water depth has experienced two deepening and three shallowing processes.The ratio of organic carbon content to S content was used to reduce the change of paleosalinity of Qingshankou Formation and Shahezi Formation.The results show that the water salinity of Shahezi Formation becomes lighter vertically,and that of Qingshankou formation becomes saltier vertically.Th/K is used to analyze the whole change of the upper Cretaceous climate.The results show that the evolution process of the upper Cretaceous paleoclimate in songke-2 well changed from dry to wet at first,and then to dry again.The application and analysis of examples show that geochemical logging makes up for the lack of lithology in drilling process,quantifies the data of rock elements and minerals,and can replace the expensive geochemical analysis data to quickly and effectively reflect the change trend of paleoenvironment.Therefore,geochemical logging,as a logging method to measure formation elements,provides an important research means and method for the analysis and study of paleoenvironmen...