松辽盆地古龙页岩微—纳米孔缝油气原位形成与富集机制

In-situ hydrocarbon formation and accumulation mechanisms of micro-and nano-scale pore-fracture in Gulong shale,Songliao Basin,NE China

通过生烃热模拟、微米与纳米CT、氩离子抛光场发射电镜、激光共聚焦和二维核磁等实验分析,对松辽盆地古龙页岩油的生成模式、储集结构与富集机制进行研究。研究表明:①古龙页岩中存在大量微微型藻、微型藻和沟鞭藻,这些形成于微咸—半咸水的藻类共同构成了富氢页岩的生油母质;②青山口组页岩生油物质大多以有机黏土复合体的形式存在,有机质在成熟演化过程中黏土矿物具有抑制和加氢催化双重作用,扩大了页岩油生成窗口的下限、增加了轻烃生成数量;③古龙页岩储集空间的形成与溶蚀和生烃作用有关,随成岩作用增强微纳米孔隙数量增加、孔隙直径变小,与页理缝发育数量增多同步,构成了古龙页岩特有的纳米级孔-微米级页理缝双重介质储集层;④古龙页岩微—纳米级储油单元具有独立的油气赋存相态,表现为小孔凝析态、大中孔气液两相(或液态)和全孔径含油的特征。古龙页岩油形成与富集机制的新认识对推进中国陆相页岩油的勘探实践具有理论指导意义。

By conducting experimental analyses,including thermal pyrolysis,micro-/nano-CT,argon-ion polishing field emission scanning electron microscopy(FE-SEM),confocal laser scanning microscopy(CLSM),and two-dimensional nuclear magnetic resonance(2D NMR),the Gulong shale oil in the Songliao Basin was investigated with respect to formation model,pore structure and accumulation mechanism.First,in the Gulong shale,there are a large number of picotype algae,microalgae and dinoflagellates,which were formed in brackish water environment and constituted the hydrogen-rich oil source materials of shale.Second,most of the oil-generating materials of the Qingshankou Formation shale exist in the form of organic clay complex.During organic matter thermal evolution,clay minerals had double effects of suppression and catalytic hydrogenation,which expanded shale oil window and increased light hydrocarbon yield.Third,the formation of storage space in the Gulong Shale was related to dissolution and hydrocarbon generation.With the diagenesis,micro-/nano-pores increased,pore diameter decreased and more bedding fractures appeared,which jointly gave rise to the unique reservoir with dual media(i.e.nano-scale pores and micro-scale bedding fractures)in the Gulong shale.Fourth,the micro-/nano-scale oil storage unit in the Gulong shale exhibits independent oil/gas occurrence phase,and shows that all-size pores contain oils,which occur in condensate state in micropores or in oil-gas two phase(or liquid)state in macropores/mesopores.The understanding about Gulong shale oil formation and accumulation mechanism has theoretical and practical significance for advancing continental shale oil exploration in China.