鄂尔多斯盆地延长组长7段页岩油形成富集机理

Formation and accumulation mechanism of shale oil in the 7th member of Yanchang Formation,Ordos Basin

页岩油是亟待开发利用的一种非常规油气资源。利用岩石地球化学和烃源岩地球化学的方法对鄂尔多斯盆地延长组长7段页岩油形成的基本条件和富集机制进行了系统分析。长7段沉积了平均残余有机碳丰度达7.4%的特高丰度富有机质泥页岩,该套泥页岩中发育丰富的微纳米孔隙,为页岩油的富集创造了良好的条件。长7段页岩油富集的主要机制包括:①高有机物生产力和强还原水体令长7段沉积期的超富营养化湖盆中的有机质得以有效保存,形成高有机质丰度的泥页岩,为页岩油形成提供了物质基础;②长7段富有机质泥页岩生油能力强、转化效率高、排油强度大,为页岩油的规模形成提供了良好条件;③有机质吸附与孔隙容留双机制的页岩油赋存方式,为页岩油的富集提供了多种方式。

Shale oil is a kind of important unconventional hydrocarbon resource in urgent need of exploitation.A systematic analysis of the forming conditions and accumulation mechanisms of shale oil in the 7 th member of the Yanchang Formation(Chang 7 member) in Ordos Basin was carried out by using petro-chemistry and source rock geochemistry methods.The results show that the oil shale deposited in the member is extremely rich in organic matter with an average residual organic carbon abundance of 7.4%,and contains well-developed micro-and nano-pores for shale oil accumulation.Three main mechanisms of shale oil accumulation in the member are brought forward in this study:(1) both high organic matter productivity and strong reducing water environment served to effectively preserve organic matters in the super eutrophic lake basin during deposition,and organic shale of high abundance developed thereby provided the material basis for shale oil generation;(2) organic-rich shale characterized by strong oil-generating capacity,high conversion efficiency,and high intensity of oil expulsion in the member provided favorable conditions for the generation of shale oil in large scale;and(3) the dual occurrence mode of shale oil,i.e.,organic matter adsorption and pore retention,provided various ways for the enrichment of shale oil in the member.