Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis
Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis
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DOI：
10.1177/0144598718763890
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发表时间：
2018-03
影响因子：
2.7
通讯作者：
Mei Han;Chao Han;Zuozhen Han;Z. Song;Wenjian Zhong;Hao Li;W. Xu
中科院分区：
文献类型：
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作者：
Mei Han;Chao Han;Zuozhen Han;Z. Song;Wenjian Zhong;Hao Li;W. Xu
页岩成岩作用中脆性矿物对页岩孔隙的影响一直存在争议，难以直接量化。然而，脆性矿物和页岩孔隙之间的关系可以提供间接指导有关成岩作用过程中的过成熟的海相页岩。通过对五峰组和龙马溪组不同总有机碳含量的泥质样品进行孔隙度分布测定，研究孔隙体积与泥质组成的关系，以区分有机质和无机矿物的孔隙度范围，研究泥质成岩作用。五峰页岩和龙马溪页岩样品由粘土矿物、方解石、白云石、石英、长石和少量组分组成。使用页岩和油母岩的氮吸附等温线分析确定的孔径分布对于小于约100 μ m的孔径显示出类似的趋势。6.5 nm，但对于较大的孔尺寸有不同的趋势。压汞饱和度表明，大孔隙占总孔隙体积的14.4-22%。根据一系列描述页岩组成与孔隙体积或孔隙度之间关系的交会图以及扫描电子显微镜观察，发现有机质孔隙包括大部分微孔-中孔（孔径< 6.5 nm）。有机质孔隙和与碳酸盐相关的颗粒内孔隙构成了中孔的大部分（孔径6.5-50 nm）。最后，与石英相关的颗粒间孔隙构成大部分大孔。与碳酸盐岩有关的中孔隙是成岩过程中溶解作用形成的，而与石英有关的大孔隙则是原始粒间孔隙的继承者。中孔体积随着碳酸盐含量的增加而增加，而大孔体积由于“孔径控制溶解度”效应而减小，这导致溶解的碳酸钙在较大的大孔中沉淀。
The effects of brittle minerals in shale diagenesis on shale pores remain controversial and it is difficult to quantify directly. However, the relationship between brittle minerals and shale pores could provide indirect guidance regarding diagenesis processes in post-mature marine shales. In this study, the pore size distribution was determined, and the relationship between pore volume and shale composition was examined in shale samples with different total organic carbon contents from the Wufeng and Longmaxi Formations, with the objective of distinguishing pore size ranges in organic matter and inorganic minerals, respectively, and studying shale diagenesis. The samples of the Wufeng and Longmaxi shales are composed of clay minerals, calcite, dolomite, quartz, feldspar, and some minor components. The pore size distributions, which were determined using nitrogen adsorption isotherm analysis of shale and kerogen, show similar trends for pore sizes less than approx. 6.5 nm but different trends for larger pore sizes. Mercury injection saturation shows that macropores account for 14.4–22% of the total pore volume. Based on a series of crossplots describing the relationships between shale composition and pore volume or porosity associated with different pore sizes as well as on scanning electron microscopy observations, organic matter pores were found to comprise most of the micro-mesopores (pore diameters < 6.5 nm). Organic matter pores and intraparticle pores associated with carbonate constitute the majority of mesopores (pore diameters 6.5–50 nm). Finally, interparticle pores associated with quartz comprise the majority of the macropores. The mesopores associated with carbonate were formed by dissolution during diagenesis, whereas the macropores associated with quartz are the remainders of the original interparticle pores. Mesopore volumes increase with increasing carbonate content while macropore volumes decrease due to the ‘pore size controlled solubility’ effect, which causes dissolved calcium carbonate to precipitate in larger macropores.