Abstract:

The below oil-reservoir combination in the southern margin of Junggar basin is playing an importantrole in the hydrocarbon exploration，thus it is necessary to focus our attention on the research on hydrocarbonpotential and expulsion efficiency of hydrocarbon of chief source. In this paper, based on the theory of hydrocarbon-expulsion threshold，models of hydrocarbon generation and expulsion of the Jurassic source rocks were established and their quantity of hydrocarbon generation and expulsion，expulsion efficiency of hydrocarbon were calculated by using the hydrocarbon-generation potential method.  The results showed that the vitrinite reflectance corresponding to hydrocarbon-expulsion threshold of both mudstone and coal seam is0.7%.The total hydrocarbon generation quantity and the total hydrocarbon expulsion quantity of the Jurassic  source rocks are 3 ,973. 84 x 108t and 1 ,402. 71 x 108t respectively. Of all the hydrocarbon expulsion quantity，69. 85 percentages of them were expulsed by the source rocks in Badaowan Formation.  The average hydrocarbon expulsion efficiencv of Jurassic source rocks is 35. 30% in the southern margin of Junggar basin.  The hydrocarbon expulsion efficiency of source rock with different series of strata and different lithology is obviously different. The hydrocarbon expulsion efficiency of mudstone is much higher than that of coal seam. In general，source rocks in the Jurassic have generated and expulsed large amounts of hydrocarbons，and the expulsion efficiency of hydrocarbon is quite high，indicating a promising resource prospect of the below oil-reservoir combination in the southern margin of Junggar basin.

Key words: expulsion efficiency of hydrocarbon, hydrocarbon-expulsion threshold, source rock;Jurassic, the below oil-reservoir combination, southern margin of Junggar basin