Study On Geochemical Features Of Mudstone From The 4^th Member Of The Palaeogene Shahejie Formation In Dongying Depression

With the increase of the global demand for energy,unconventional oil and gas resources is becoming increasingly highlighted.Lacustrine shale oil and gas as a kind of important form of unconventional oil and gas resources,it is more and more important.As a representative continental lacustrine basin,the Dongying depression has developed a large set of lacustrine shale,which can be used as a typical sample for the study of continental lacustrine shale in eastern China.Therefore,the study of lacustrine shale oil and gas in Dongying depression is of great significance.In this paper,a series of systemic researching work has been developed on lithology distribution,mineral and element composition of the mud shale in Sha-4 member in Dongying depression,which could provide a reference for the exploration and development of shale oil and gas resources in the study area.On the basis of the extensive collection of drilling,logging,formation,existing mineral element and other related data,large number of tests have been done to the mud shale of Sha-4 member in Dongying depression,including low-temperature liquid nitrogen adsorption,the methane isothermal adsorption experiment,X-RD diffraction rock identification,inductively coupled plasma atomic spectroscopy,scanning electron microscopy,energy spectrum and so on.The following conclusions are obtained: 1)according to mineral composition and presence of bedding,the mud shale of Sha-4 member in Dongying depression can be divided into clay rock,calcareous mudstone,calcareous shale,oil shale and marl,showing heterogeneity in lithologic distribution;2)from the edge of the basin to the sedimentary center,water salinity increased gradually,the oxidation sedimentary environment transited to anoxic environment,sequentially depositing gray shale,marl,argillaceous gypsum layer,salt mud shale and salt rocks,forming a co-deposition phenomenon of evaporite and mudstone;3)Sha-4 member deposited in the shallow lake environment of dry climate evaporation phase,the measured element analysis results show that the element enrichment regularity of oil shale and mudstone section is different,both the distribution of elements content in profile and plane showed heterogeneity;4)biomarker and its characteristic parameter analysis results of source rocks in Sha-4 member show that the organic parent material is multi-source,and the sedimentary environment of the Sha-4 member is more reductive than that of the Sha-3 member,for brackish water-salt water lake facies.