Development Characteristics and Formation Mechanism of Intra-Organic Reservoir Space in Lacustrine Shales
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摘要: 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2 500~4 000 m, 该类孔隙连续分布, 当埋深小于3 600 m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.Abstract: 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-6700f field 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 m to 4 000 m, the pores continuously exist. At the depths less than 3 600 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 organic 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.
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Key words:
- lacustrine shale /
- oil window /
- organic reservoir space /
- organic acid /
- formation mechanism /
- petroleum geology.
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图 1 研究区构造单元及取样点分布
图a中虚线表示隆起
Fig. 1. Structure units and sample distribution of the study area
图 2 东营凹陷有机质-粘土-碳酸盐混合体电子图像和能谱图
a.2号样品富含有机质泥质纹层和富含碳酸盐纹层间充填有机质(LFD)及其能谱图，wang129，Es4s，TOC=3.97%，Ro=0.32%；b.5号有机质(C)、粘土(I/S)、碳酸盐(Cc)混合体中发育的孔隙(BSED)及其能谱图，yong89，Es4s，TOC=2.85%，Ro=0.53%；c.7号黄铁矿、石英、方解石颗粒间孔内充填含有机质粘土碳酸盐混合体(BSED)及其能谱图，fan291，Es3x，TOC=9.20%，Ro=0.62%；d.11号有机质、粘土、碳酸盐混合体中发育的孔隙(LFD)及其能谱图，li673，Es3x，TOC=1.74%，Ro=0.82%.上图为电子图像；下图为能谱图
Fig. 2. OM-clay-carbonate complexes in the Dongying sag
图 3 东营凹陷有机质-粘土-硫酸盐混合体电子图像和能谱图
a.9号白云石D晶间孔中充填含有机质、粘土Clay的硫酸盐Su矿物及其能谱图，fengshen1，Es4s，TOC=2.30%，Ro=0.70%；b.1号页岩低成熟阶段有机质与矿物的接触关系，wang33，Es4s，TOC=4.48%，Ro=0.39%；c.2号页岩低成熟阶段有机质与矿物的接触关系，wang129，Es4s，TOC=3.97%，Ro=0.32%；d.3号页岩低成熟阶段有机质与矿物的接触关系，liang206，Es4s，TOC=3.43%，Ro=0.49%；e.6号页岩片状伊蒙混层间充填了有机质，feng112，Es3x，TOC=6.85%，Ro=0.53%
Fig. 3. OM-clay-sulfate complexes in the Dongying sag
图 4 东营凹陷沙四上亚段页岩富含有机质矿物混合体孔隙电子图像和能谱图
a.2号有机质、粘土、碳酸盐混合体中发育的孔隙，wang129，Es4s，TOC=3.97%，Ro=0.32%；b.4号方解石、有机质和粘土混合体中发育孔隙，lai109，Es4s，TOC=5.31%，Ro=0.43%；c.8号有机质、粘土、碳酸盐混合体中发育的孔隙，niu872，Es3x，TOC=7.03%，Ro=0.55%；d.9号有机质、粘土、碳酸盐混合体中发育的孔隙，fengshen1，Es4s，TOC=2.30%，Ro=0.70%；e.10号有机质、粘土、碳酸盐混合体中发育的孔隙，wang78，Es3x，TOC=3.41%，Ro=0.66%；f.11号有机质、粘土、碳酸盐混合体中发育的孔隙，li673，Es3x，TOC=1.74%，Ro=0.82%；g.12号有机质、粘土、碳酸盐混合体中发育的孔隙，wang78，Es4s，TOC=3.63%，Ro=0.70%；h.13号硫酸盐有机质和粘土的混合体中发育的孔隙，li673，Es4s，TOC=3.49%，Ro=1.09%.C.有机质；I/S.伊蒙混层；Clay.粘土；Cc.方解石；Su.硫酸盐；Pr.黄铁矿；D.白云石；Q.石英
Fig. 4. Pores in the Upper Es4 shales rich in OM-mineral complexes in the Dongying sag
图 6 不同湖相环境烃源岩生排烃模式差异
Fig. 6. Different schemes of hydrocarbon generation and expulsion in lacustrine shales
图 7 东营凹陷不同层位页岩甲酸根随埋深关系
Fig. 7. Relationship between formate in different shales and depth
图 8 东营凹陷不同层位页岩乙酸根随埋深关系
Fig. 8. Relationship between acetate in different shales and depth
图 9 东营凹陷页岩孔隙度随埋深变化关系
Fig. 9. Relationship between porosities and depths of shales in Dongying sag
表 2 东营凹陷沙四上亚段不同埋深页岩有机酸含量统计
Table 2. Statistics of organic acid contents in the Upper Es4 shales at different depths in the Dongying sag
编号 层位 埋深(m) 沥青“A”(μg/g) 族组成(%) 沥青酸(%) 干酪根酸(%) 烷烃 芳烃 非烃 沥青 SL952 Es4 1 138 2 476 9 5 80 6 0.036 5 0.016 3 SL953 Es4 1 341 11 253 10 8 70 12 0.102 6 0.032 2 SL954 Es4 2 021 1 454 16 7 70 7 0.016 6 0.014 9 SL955 Es4 2 605 8 294 50 15 29 6 0.029 5 0.020 3 SL957 Es4 3 608 5 049 35 15 41 9 0.002 0 0.008 5 
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表 3 LH973页岩样品有机酸热模拟结果
Table 3. Thermal simulation results on organic acid in LH973 shale
样品 沥青/岩 沥青酸/岩 干酪根酸/岩 原样 2.470 0.400 0.102 175 ℃样 0.178 0.038 0.075 250 ℃样 0.169 0.024 0.011 300 ℃样 0.736 0.064 0.050
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表 4 东营凹陷古近系泥页岩中游离态有机酸含量统计
Table 4. Statistical contents of free state organic acid in the Paleogene shales in the Dongying sag
层段 含量(μg/g) 乙酸根 甲酸根 草酸根 最小 最大 平均 最小 最大 平均 最小 最大 平均 Es3x 2.55 51.40 16.98 0.62 56.55 10.36 1.96 9.16 4.27 Es4s 0.00 69.06 19.49 3.38 45.42 14.64 0.00 6.56 4.14 Es4x 0.00 46.08 22.09 2.31 27.48 12.42 2.41 7.16 4.34
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