基于氮气吸附法的渝东南下寒武统页岩孔隙的分形特征

Fractal Characteristics of Pore Structure of Lower Cambrian Shale in Southeast Chongqing Using Nitrogen Adsorption Data

分形维数是多孔介质不规则程度的度量，以渝东南下寒武统页岩的氮气吸附法测量结果为研究对象，采用FHH模型的分形维数计算方法，得到渝东南下寒武统页岩的分形维数。研究结果表明，渝东南下寒武统页岩孔隙的分形维数具有明显孔径分界点，即具有双重分形特征，小孔隙分形维数凸变化范围在2．3559～2．6577。平均值为2．488。大孔隙分形维数D2变化范围在2．5971—2．8746，平均值为2．7631；大孔隙分形维数的平均值大于小孔隙分形维数的平均值。说明大孔隙结构的复杂程度大于小孔隙结构的复杂程度；页岩孔隙的分形维数与有机碳（TOC）含量、吸附气量、比表面积和孔容呈正相关，其中与孔隙的比表面积和孔容的相关性显著。而与黏土矿物含量呈弱负相关。

The fractal dimensions of pore structure of shale in the southeast Chongqing are calculated using the FHH model based on measured results of the pore structure by nitrogen adsorption. The result shows that the fractal dimensions of pore structure of shale in the southeast Chongqing obviously have the aperture boundary point, that is to say, have the dual fractal feature. The fractal dimension values of the big pore structure are 2.3559-2.6577, with an average of 2.488, and the fractal dimension values of the small pore structure are 2.5971-2.8746, with an average of 2.7631. The small pore structure, with a larger fractal dimension value, shows a higher degree of complexity than the large pore structure. There is a positive correlation among the ~ractal dimension values of shale pore structure and TOC content, gas adsorption, specific surface area and pore volume. Especially, it is found that the fractal dimension values show a significantly positive correlation with the specific surface area and pore volume. Whereas, there is a negative correlation between the fi-actal dimension values of shale pore structure and clay mineral content.