Pore characterization of organic-rich Late Permian Da-long Formation shale in the Sichuan Basin, southwestern China
Pore characterization of organic-rich Late Permian Da-long Formation shale in the Sichuan Basin, southwestern China
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四川盆地晚二叠世大龙组富有机质页岩孔隙特征
DOI：
10.1016/j.fuel.2017.09.068
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发表时间：
2018
期刊：
影响因子：
7.4
通讯作者：
Liang Xu
中科院分区：
文献类型：
--
作者：
Zhifu Wei;Yongli Wang;Gen Wang;Zepeng Sun;Liang Xu
中国南方晚二叠世大龙组页岩被视为页岩气藏目标。但页岩气藏基础资料的缺乏增加了天然气勘探的难度。为了解页岩孔隙结构特征，对川西北广元地区上寺剖面大龙组样品进行了总有机碳（TOC）含量、X射线衍射（XRD）、场发射扫描电镜（FE-SEM）和低压N2吸附-解吸分析等实验。结果表明，大龙组样品TOC含量差异较大，范围为0.14%~14.40%，平均值为3.60%。剖面中部附近发育黑色页岩层，TOC 含量较高，为 1.20%～14.40%。矿物基质的主要成分是碳酸盐矿物和石英矿物。富含有机质页岩的 TOC 含量与石英含量之间观察到弱正趋势，表明这些大龙页岩样品中的石英至少部分是生物成因的。有限元扫描电镜观察，大龙黑色页岩矿物基质和有机质孔均发育，并发育少量页间孔、页内孔及裂缝孔。此外，随着TOC含量的增加，由于OM延展性，富有机质页岩的孔径分布（PSD）曲线逐渐减小。在页岩样品中测量了双峰 PSD 与表面积以及单峰 PSD 与孔隙体积的关系，表明表面积主要与微孔和细中孔（<10 nm）相关，而较大的孔隙是孔隙体积的主要贡献者。因此，该页岩气储层的孔隙网络主要与有机质相关，尤其是小孔隙，而矿物成分预计是造成较大孔隙的原因。
The Late Permian Da-long Formation shale in southern China is regarded as a shale gas reservoir target. However, the lack of fundamental data for shale gas reservoirs increases the difficulty of gas exploration. To understand the pore structure characteristics of these shales, a series of experiments was conducted on Da-long Formation samples collected from the Shangsi Section in the Guangyuan area in the Northwest Sichuan Basin, southwestern China, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and low-pressure N2adsorption-desorption analyses. The results show that TOC contents vary greatly between the Da-long Formation samples, ranging from 0.14% to 14.40% with an average value of 3.60%. A black shale layer occurs near the middle of the section with a relatively high TOC content ranging from 1.20% to 14.40%. The major components of the mineral matrix are carbonate and quartz minerals. A weakly positive trend between the TOC content of organic-rich shales and the quartz content was observed, indicating that the quartz in these Da-long shale samples is at least partially of biogenic origin. Both mineral matrix and organic matter pores are developed in Da-long black shales, as observed by FE-SEM, along with a few interP and intraP pores and fracture pores. Additionally, with increasing TOC content, the pore size distribution (PSD) curves of organic-rich shale gradually decrease as a result of OM ductility. Bimodal PSD versus surface area and unimodal PSD versus pore volume were measured in the shale samples, indicating that surface area is mainly associated with micropores and fine mesopores (<10 nm) and larger pores are the dominate contributor to pore volume. Therefore, the pore network in this gas shale reservoir is predominantly associated with organic matter, especially small pores, and the mineral compositions are expected to be responsible for larger pores.
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