Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao, 266580, PR China.
Research Institute of Petroleum Exploration & Development, Beijing, 100083, PR China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):274-283. doi: 10.1166/jnn.2021.18885.
The fractal characteristics of marine shale from the Middle-Upper Ordovician Wulalike Formation (O₂w) in the southwest margin of the Ordos Basin are studied. Based on low-temperature nitrogen adsorption experiments, the FHH (Frenkel-Halsey-Hill) model was employed to investigate the relationship between the marine shale composition, such as TOC, mineral content and shale gas content, and pore structure parameters, such as BET specific surface area, average pore diameter, porosity and fractal dimension. The results show that the pore size distribution curve of shale slowly decreased after the pore size was greater than 50 nm, the pore size distribution showed multiple peaks, and the peak value was mainly in the range of 2-10 nm. Most pores are nanopores, although the pore type and shape are different. Two different fractal dimensions and ₂ are obtained from the two segments with relative pressures of 0-0.5 and 0.5-1.0, respectively: the range is 2.77-2.82, and the ₂ range is 2.63-2.66. As is larger than ₂, the pore structure of small pores is more uniform than that of large pores in the shale samples. The relationship between the fractal dimensions and ₂ and the total organic carbon (TOC) content is a convex curve. Fractal dimension reaches its maximum when TOC is 0.53 wt.%. Fractal dimension decreases with increasing specific surface area, porosity and average pore size. The fractal dimension has a different influence on the gas storage and migration in shale; the larger the fractal dimension is, the stronger the heterogeneity and the more complex the pore structure, and this outcome is conducive to the storage of gas in shale but not beneficial to the permeability and production of gas.
研究了鄂尔多斯盆地西南缘中上奥陶统乌拉力克组（O₂w）海相页岩的分形特征。基于低温氮吸附实验，采用 FHH（Frenkel-Halsey-Hill）模型研究了海相页岩组成（如 TOC、矿物含量和页岩气含量）与孔隙结构参数（如 BET 比表面积、平均孔径、孔隙度和分形维数）之间的关系。结果表明，页岩的孔径分布曲线在孔径大于 50nm 后缓慢下降，孔径分布呈多峰分布，峰值主要在 2-10nm 范围内。大多数孔隙为纳米孔，尽管孔隙类型和形状不同。从相对压力为 0-0.5 和 0.5-1.0 的两个段中，分别得到了两个不同的分形维数 和 ₂： 范围为 2.77-2.82， ₂范围为 2.63-2.66。由于 大于 ₂，页岩样品中小孔的孔结构比大孔更均匀。分形维数 和 ₂与总有机碳（TOC）含量之间的关系是凸曲线。当 TOC 为 0.53wt.%时，分形维数 达到最大值。分形维数 随着比表面积、孔隙度和平均孔径的增大而减小。分形维数对页岩中气体的存储和运移有不同的影响；分形维数越大，非均质性越强，孔隙结构越复杂，这有利于气体在页岩中的存储，但不利于气体的渗透率和产量。
