基于氩气吸附的页岩纳米级孔隙结构特征

为了研究页岩储层微观孔隙结构特征，以川南地区龙马溪组页岩为研究对象，应用场发射扫描电镜（FE-SEM）定性描述页岩镜下孔隙形态及确定其类型，创新使用低温氩气（Ar）吸附实验测量页岩样品的比表面积、孔体积以及孔径分布，实现了页岩小于100 nm（纳米级）孔隙的连续测量，并根据FrenkelHalsey-Hill（FHH）模型研究了页岩孔隙结构的分形特征，探讨了有机质对页岩孔隙结构及分形特征的影响。结果表明：川南地区龙马溪组页岩储层主要发育有机质孔、粒间孔及粒内孔，并以有机质孔为主。Ar吸附等温线表明，纳米级孔隙以狭缝型为主，孔径主体分布在10 nm以下的微孔和介孔中，呈“三峰”特征，微孔主要集中在0.6～0.9 nm以及1.8～2.0 nm，介孔主要集中在4.0～5.0 nm。纳米级孔隙分形维数为2.55～2.64，表现出较强的非均质性。有机碳（TOC）含量控制了页岩纳米级孔隙的发育，TOC含量的增加使得页岩中微孔及其所占比例增高，分形维数增大，孔隙结构趋于复杂，有利于页岩储层吸附能力的增强。该研究成果对川南地区龙马溪组页岩储层纳米级孔隙结构特征研究具有重要意义。

Nanopore structure characteristics of shale based on Ar adsorption

The microscopic pore structure has direct effect on gas bearing property of shale. Field emission scanning electron microscope (FE-SEM)was applied to describe pore morphology and types qualitatively of Longmaxi shale samples in south Sichuan Basin. Low temperature Ar adsorption experiment was carried out to measure the specific surface area (SSA), pore volume (PV) and pore size distribution (PSD) of the shale samples, and the continuous measurement of nanopore less than 100 nm was achieved. Fractal characteristics of nanopore structure were also studied by use of Frenkel-Halsey-Hill (FHH) model, and the relationships among total organic carbon content, pore structure parameters and fractal dimensions were discussed. The result shows that organic pores, intergranular pores and intragranular pores are developed in Longmaxi shale, and organic pores are dominated. The nanopores are slit shape on the Ar adsorption isotherms, and are mainly distributed in micropores and mesopores less than 10 nm, and the micropore size is mainly 0.6-0.9 nm and 1.8-2.0 nm, while the mesopore size is mainly 4.0-5.0 nm. The fractal dimension of nanopores ranges from 2.55 to 2.64, showing strong heterogeneity. Total organic carbon content controls the development of nanopores in shales. With the increase of TOC content, the number and proportion of micropores increase, and the fractal dimension also increases. All these factors complicate the pore structure of shale samples, and enhance the gas adsorption capacity of shale reservoirs. The research results have important significance for the study of nanopore structure of Longmaxi shale reservoir in southern Sichuan Basin.