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页岩孔隙结构特征研究对页岩含气性评价具有重要意义。以上扬子东南缘南皋剖面下寒武统牛蹄塘组页岩储层为例,应用场发射环境扫描电子显微镜观察了页岩纳米级孔隙微观形态,通过低温氮气吸附法测定了页岩的氮气吸附等温线,并结合X-衍射矿物定量分析和有机碳含量测定,探讨了纳米级孔隙发育的控制因素。研究结果表明:矿物成分主要为黏土矿物(伊利石和少量绿泥石)、石英、长石、重晶石和石膏等。石英含量相对较高且沿剖面向上降低,wB平均为53%;相反,黏土矿物含量较低且沿剖面向上增加,wB平均为34%;碳酸盐矿物较少,仅在顶部可见。页岩主要发育粒内孔、粒间孔、裂缝和有机质孔4种孔隙类型,其中前两者较为常见。根据氮气吸附-脱附曲线、孔径分布特征、孔体积和比表面积可将样品划分为4类黑色页岩,孔隙以似片状颗粒组成的非刚性聚合物的槽状孔为主,前3类黑色页岩的孔径分布呈双峰形态,第4类黑色页岩的孔径分布呈单峰形态,最可几孔径分别为d≈0.9nm和d≈3.5nm。孔体积在0.002 8~0.024 3cm3/g之间,平均为0.014 7cm3/g,比表面积在1.056 8~28.825 0m2/g之间,平均为17.541 8m2/g,4类黑色页岩微孔频率分布依次减小,而介孔和宏孔频率分布逐渐增加,即微孔性逐渐变差,至第4类黑色页岩几乎只有宏孔孔隙。有机质丰度和矿物组分控制丹寨南皋牛蹄塘组黑色页岩的孔隙发育,其中有机质有利于孔隙发育且有机质微孔是孔体积和比表面积的主要贡献者;石英有利于孔隙发育,而黏土矿物则降低黑色页岩的孔隙性;它们均主要通过控制微孔和介孔的发育来控制黑色页岩的孔隙发育。
The study of shale pore structure is of great significance for gas evaluation of shale. Taking the Lower Cambrian Niutitang Formation shale reservoir in the Nangao section of the southeastern margin of the Yangtze River as an example, the microscopic morphology of shale nano-scale pores was observed by using a field emission scanning electron microscope. The nitrogen in shale was determined by low temperature nitrogen adsorption Adsorption isotherms, and combined with the quantitative analysis of X-ray diffraction and determination of organic carbon content, discussed the controlling factors for the development of nano-scale pores. The results show that the mineral components are mainly clay minerals (illite and a small amount of chlorite), quartz, feldspar, barite and gypsum. Quartz content is relatively high and decreases along the profile upward, with an average wB of 53%. On the contrary, the clay mineral content is lower and increases along the profile upwards with an average wB of 34%; carbonate minerals are less and only visible at the top. Shale mainly develops four kinds of pore types: intragranular pores, intergranular pores, fractures and organic pores, of which the first two are common. According to the nitrogen adsorption-desorption curve, pore size distribution, pore volume and specific surface area, the samples can be divided into four types of black shales. The pores are dominated by groove-like pores of non- The pore size distribution of black shale is bimodal, and the pore distribution of black shale of type 4 presents a single peak morphology. The most probable pore diameters are d≈0.9nm and d≈3.5nm, respectively. The pore volume is 0.002 8 ~ 0.024 3cm3 / g, the average is 0.014 7cm3 / g, the specific surface area is 1.056 8 ~ 28.825 0m2 / g, the average is 17.541 8m2 / g. Decreases, while the frequency distribution of mesopores and macropores increases gradually, that is, micropore properties gradually deteriorate, and macropores of macroscopic pores in Class 4 black shale are almost the same. Organic matter abundance and mineral composition control the porosity of black shale in Nantong, Niutao Nangao, Danzhai. The organic matter is conducive to pore development and the microporous organic matter is the main contributor to the pore volume and specific surface area. Quartz is favorable for pore development, Clay minerals, on the other hand, reduce the porosity of black shales. Both control the pore development of black shales mainly by controlling the development of micropores and mesopores.