鄂尔多斯盆地中部地区长7烃源岩特征

Characteristics of Chang7 Source Rocks in the Middle of Ordos Basin

鄂尔多斯盆地晚三叠世长7期发育了一套半深湖-深湖相优质油源岩,是该盆地最主要的烃源岩。运用有机地球化学和有机岩石学相结合的方法,对鄂尔多斯盆地中部地区长7烃源岩进行了较系统的研究。鄂尔多斯盆地中部地区长7烃源岩在研究区内广泛分布,厚度分布在3～85 m之间,普遍分布在10～50 m间,整体上呈由研究区西南部向北、向东变薄的趋势;长7烃源岩有机质丰度较高,TOC值大部分超过1.0%,生烃潜力值大部分高于6.0 mg/g,氯仿沥青"A"值大部分高于0.1%,大部分属于"好"烃源岩级别;长7的烃源岩有机质类型主要为Ⅰ和Ⅱ1型,少量为Ⅱ2和Ⅲ型;长7的烃源岩镜质组反射率Ro值在0.54%～0.92%之间,最高热解峰温Tmax值在411～456℃之间,多数已处成熟生油气阶段。

A suit of high-quality source rock of semi-deep to deep lacustrine facies developed during the age of the seventh member of yanchang formation(Chang7) at late triassic in Ordos basin,which is the most important source rock in Ordos basin.Through using organic geochemistry and organic petrology,the source rocks of Chang 7 in the middle of Ordos basin were systematically studied.The source rocks of Chang7 in the middle of Ordos basin are widespread,whose thickness is in the range of 3～85 m,generally in the range of 10～50 m,and has the trend of gradually thinning from southwest to north and east on the whole.The organic matter abundance of the source rocks of Chang7 in the middle of the Ordos Basin is higher,and its content of TOC generally exceeds 1.0%,and hydrocarbon generation potential generally exceeds 6.0 mg/g,and chloroform bitumen'A' generally exceeds 0.1%,so it belongs to better hydrocarbon source rocks.The organic matter of the source rocks of the Chang 7 member in the middle of the Ordos basin is mainly typeⅠandⅡ1 and small amount is type Ⅱ2 and Ⅲ.The vitrinite reflectance Ro of the source rocks of the Chang 7 member in the middle of Ordos basin is in the range of 0.54%～0.92%,and their highest pyrolysis peak temperature Tmax is in the range of 411～456 ℃,and most of the organic matter has been in maturation hydrocarbon generation stage.