The Genetic Types of Crude Oils and the Petroleum Geological Significance of the Fengcheng Formation Source Rock in Hashan Area,Junggar Basin

Based on GC and GC-MS analyses of crude oil(oil sand)samples in different geological unit sandlayers of Hashan area in the northern of Junggar Basin,the geochemical characteristics of crude oil and source rocks were systematically studied.According to organic matter types,sedimentary environment,maturity,and C20,C21,C23tricyclic diterpane distribution,the crude oils were divided into three genetic types. The Group I mainly distributed in the marginal overlap zones and the shallow of thrust-napped belt,and they were mainly originated from the Fengcheng Formation and experienced severe biodegradation,and they display characteristics of incomplete distribution of n-alkanes,ascendingtype tricyclic diterpanes distribution and high contents of gammacerane andβ-carotane.The GroupⅡ mainly distributed in the middle and deep of the thrust-napped belt and was generated early in the low-mature stage of Fengcheng Formation source rocks,and the saturated hydrocarbon chromatograms of the oil is distributed fully indicating slight or non-biodegradation with obviously higher content of phytane than pristine andascendingtype tricyclic diterpanes distribution.The GroupⅢ mainly distributed in the Xishanyao Formation in the marginal overlap zones in wellblock of Haqian 20and was mainly from the high-mature Wuerhe Formation source rocksassisted by the Fengcheng Formation source rocks.The crude oil with pristine prevalence,low contents of gammacerane andβ-carrotenes anddescendingtype distribution of C20,C21,C23tricyclic diterpanes.Based on the geological modeling foothill belt and analysis of structural evolution of Hashan,it is believed that the Fengcheng Formation source rocks could extend northward to the Daerbute fault,and the distribution area up to 1 000km2 is larger than original,which will give practical guide to expanding the oil and gas exploration domains in the northern Junggar Basin.