Evaluaton and hydrocarbon expulsion characteristics of the Middle-Lower Jurassic source rock in the southern margin of Junggar basin

There are a few exploration wells drilled through the Middle-Lower Jurassic source rock in the southern margin of Junggar basin.Thus,it is difficult to understand the resource potential.Based on the comprehensive analysis of geological and geochemical characteristics of single well,seismic inversion,sedimentary facies,tectonic burial depth,etc.,this paper predicts the horizontal distributions of the following aspects: the thickness of source rock,abundance and type of organic matter,etc.Further,utilizing the method of hydrocarbon generation potential establishes the hydrocarbon expulsion models of the Middle-Lower Jurassic source rock.Besides,this research evaluates the resource potential.Because of that,it is safe to conclude that it is of great significance to explore the lower oil and gas assemblage in the southern margin of Junggar basin.The results show that,source rocks in the Middle-Lower Jurassic distribute widely,with huge thickness and relatively high abundance of organic matter;the main types of organic matter are mainly III and II2 which are in the mature-high mature evolution stage.The vitrinite reflectance,which is corresponding to hydrocarbon-expulsion threshold of mudstone and coal seam,is 0.7%.The source rocks began to enter into hydrocarbon expulsion period in the late Cretaceous,and peak value of the hydrocarbon expulsion is from Neogene to present.The total quantities of hydrocarbon expulsion and perspective resources are 140.27 Gt and 12.54 Gt,respectively.Specifically,the oil resources is 10.52 Gt,and the gas resources is 2.28 Tm3.In general,source rocks in the Middle-Lower Jurassic have expulsed large amounts of hydrocarbons,and the source rocks expelled hydrocarbon in the late period,indicating a promising resource prospect.