Geological Characteristic And Minerogenetic Condition Of Oil Sand In Western Qaidam Basin

With the increasing difficulty of conventional oil and gas exploration in China,the need for oil and gas resources is also becoming more and more serious.The increasing dependence on oil import makes unconventional oil and gas,including oil sands,more and more important.Chinese oil sand resources are mainly distributed in west basin including Qaidam basin.The western qaidam basin is the richest area of oil and gas resources in the basin.Therefore,the oil sand in west of qaidam basin is the first choice to study oil sands resources in Qaidam basin.Based on the sedimentary structural evolution and regional geological background in the Palaeogene and Neocene of west Qaidam basin,this paper makes clear the thickness and distribution of oil sands in the research area by outcrop,and make sure the oil sand's characteristics of petrology,physical property,oiliness through the ordinary thin slice and the fluorescence thin slice from core.seismic data are utilized to study the structure of oil sand.The quality and source of oil are studied through geochemical tests.Finally we will get geological characteristics and metallogenic factors of oil sand in western Qaidam basin for providing the basis for further oil and gas exploration.The investigation indicates that oil sand mainly expose in the high part of honggouzi,along the limbs of the anticline,which lower Youshashan formation(N21)and upper Youshashan formation(N22)mainly develop in this region.oil sand are mostly lithic arkoses and feldspathic litharenites with a low maturity.The oil sand in western qaidam basin is middle-low permeable and middle-low porous reservoir.Mean oil content ranging from 2.5-5%?The content of saturated hydrocarbons in sand oil is very high,which is about 67.07%.the Aromatic hydrocarbon content is about 13.35%;The nonhydrocarbon component is about 17.37%.The characteristics of saturated hydrocarbon biomarkers indicate that the source of the sand oil is the salt water lake aquatic organism,and its source rock is the Tertiary source rock in western Qaidam basin.The original conventional oil and gas reservoir laid the foundation for the formation of the oil sands,the timing of the tectonic movement controlled the structure of oil sands,oil-rich sag and the hydrocarbon properties control the mining area of oil sands and oil content,the distribution of reservoir characteristics control the distribution of sand oil and the limit of oil content,cap rock characteristics and reservoir cap association controls the oil sands oil content lower limit,The fault provides a migration channel for the formation of oil sands.