Pore characteristics of lacustrine shale within the oil window in the Upper Triassic Yanchang Formation, southeastern Ordos Basin, China
Pore characteristics of lacustrine shale within the oil window in the Upper Triassic Yanchang Formation, southeastern Ordos Basin, China
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DOI：
10.1016/j.marpetgeo.2018.01.013
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发表时间：
2018-03
影响因子：
4.2
通讯作者：
Huijuan Guo;Ruliang He;W. Jia;P. Peng;Yuhong Lei;Xiaorong Luo;Xiangzen Wang;Lixia Zhang;
中科院分区：
文献类型：
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作者：
Huijuan Guo;Ruliang He;W. Jia;P. Peng;Yuhong Lei;Xiaorong Luo;Xiangzen Wang;Lixia Zhang;
延长组富含有机质的页岩是我国湖相地层中最有前途的页岩油气混合体系。泥岩孔隙主要位于含油窗口内，孔隙类型和分布受多种因素的影响，包括排油和滞留、矿物和有机质组成以及压实作用。为了更好地了解有机质孔隙发育的控制因素，选取了延长组长7段和长9段10个不同有机质含量的岩心样品进行孔隙表征。该研究结合了显微镜观察，无论是薄切片和离子研磨表面的样品与低压二氧化碳和氮气吸附和体积孔隙率测量，主要重点是OM相关的孔隙。所选样品通常具有相对较低的总孔隙度，与孔连接不良。在海相页岩中发现的大多数孔隙类型都存在。多孔OM的尺寸通常很小，大多数测量为几百纳米到几微米，这表明孔隙发育的一般压实效应。孔隙发育与不同的排油过程有关。具有非常多孔的有机质的页岩是一个非常重要的特征。与荧光lipitinites共存的OM存在于一个交联的结构，可能与改变细胞外聚合物（EPS）的压实和成熟。不同的OM类型，在大小和形状上都不包含任何可见的孔隙（如木质文物，迁移固体沥青和OM纹层与粘土矿物密切相关）。不寻常的低介孔和大孔体积的样品中，总有机碳（TOC）含量最高的确认OM纹层的优势，没有可见的孔隙，但是，丰富的微孔CO2吸附分析表明。该样品中的中孔和大孔可能由于显著的压实效应而未形成。由于研究的样品数量较少，因此需要谨慎看待这些OM孔隙特征。
Organic matter (OM)-rich shale in the Yanchang Formation is recognized as a promising hybrid shale oil/shale gas system in lacustrine strata in China. Being mainly in the oil window, both the type and distribution of the pores in the shale have been affected by several factors, including petroleum expulsion and retention, mineral and organic composition, and compaction. To obtain a better understanding of the factors controlling OM pore development, 10 core samples were selected with various OM content from the Chang 7 and Chang 9 members of the Yanchang Formation for pore characterization. The investigation combined microscopic observation, both of thin sections and ion milled surfaces of samples with low-pressure carbon dioxide and nitrogen adsorption and bulk porosity measurements, with the main emphasis being on OM-associated pores.The selected samples generally have relatively low total porosity, with the pores being poorly connected. Most pore types found in marine shales were present. The size of porous OM is usually small, mostly measuring several hundreds of nanometers to a few micrometers, which suggest a general compaction effect on pore development. The pore development is related to different petroleum expulsion processes. Shale with very porous OM was a very important feature. The OM coexisting with fluorescent lipitinites was present in a cross-linked nanofiber structure, possibly related to altered extracellular polymeric substances (EPS) by compaction and maturation. Various OM types that varied in both size and shape did not contain any visible pores (e.g. woody relics, migrated solid bitumen and OM laminae in close association with clay minerals). Unusually low meso- and macropore volume in the sample with the highest total organic carbon (TOC) content was confirmed by the predominance of OM laminae without visible pores; however, abundant micropores were indicated by CO2adsorption analysis. Meso- and macropores in this sample had probably not developed due to a significant compaction effect. Due to the small numbers of studied samples, these OM pore characteristics need to be viewed with caution.