湖相页岩有机储集空间发育特点与成因机制

Development Characteristics and Formation Mechanism of Intra-Organic Reservoir Space in Lacustrine Shales

有机储集空间是页岩的重要储集类型,但对处于生油窗内的湖相页岩是否发育有机储集空间却缺少研究.系统采集处于生油窗范围内不同演化程度的湖相页岩样品,利用氩离子抛光样品制备技术,分别使用Quanta200扫描电镜及EDAX能谱仪联机和JSM-6700f冷场发射扫描电子显微镜对湖相页岩进行微观特征观察和岩石组分分析,背散射图像和二次电子图像均显示,页岩内大量发育呈暗色条带状的有机质-粘土-碳酸盐和有机质-粘土-硫酸盐混合体.该混合体内极易发育孔隙,从2 500~4 000m,该类孔隙连续分布,当埋深小于3 600m时,这类孔隙的尺度一般为微米级,但随着演化程度增高纳米孔隙增加,并且呈密集分布.混合体内孔隙的发育分别与页岩含油饱和度迅速增高及游离有机酸含量的增加同步,该类孔隙的发育不仅仅取决于生烃作用,它的形成是生烃转化和有机酸溶蚀共同作用的结果.上述结果表明,在生油窗范围内湖相页岩中,有机质与无机矿物作为整体共同演化且相互作用,在生烃与溶蚀叠合作用下形成了丰富的有机质-矿物混合体内储集空间,该储集类型对陆相页岩油气赋存具有重要意义.

Organic reservoir is one of the important reservoir types in shale.The development of organic reservoir space in lacustrine shales within oil window is lack of research work.In view of this,lacustrine shale samples with different maturities in oil window were selected and prepared by argon ion-milling techniques.Joint Quanta200 scanning electron microscope and EDAX energy spectrometer,and JSM-6700 ffield emission scanning electron microscope were employed to observe the microstructure and analyze the composition of lacustrine shales.Both back scattered images and secondary electronic images show that abundant mixtures of dark banded organic matter（OM）-clay-carbonate and OM-clay-sulfate were developed in shales.Pores were easily developed in the mixtures.From 2 500 mto 4 000 m,the pores continuously exist.At the depths less than 3600 m,the pore size generally occurs on micron scale.With the continued evolution,nano pores increase and are densely distributed.The intra-pores in the mixtures are synchronous with the rapid increasing of oil saturation and the rising of free organ-ic acids in shales,respectively.The development of the pores not only depends on the hydrocarbon generation,but also on the interaction of hydrocarbon conversion and the organic acid dissolution.The results indicate that in lacustrine shales within oil window,organic matter and inorganic minerals undergo evolution as a whole and interact with each other.The combination of hydrocarbon generation and dissolution form abundant reservoir space in the hybrid of organic matter and minerals,which has important significance to the occurrence of oil and gas in continental shales.