川南龙马溪组页岩孔隙结构综合表征及其分形特征

为了科学评价川南地区龙马溪组页岩孔隙发育特征对页岩气赋存与流动过程的影响，综合采用压汞、液氮吸附及二氧化碳吸附等测试方法，对页岩孔隙结构进行全尺度表征，并对不同尺寸的孔隙进行分形拟合，计算综合分形维数，最后结合地球化学和矿物组成对综合分形维数的影响因素进行探讨。结果表明：页岩样品孔径分布呈多峰态，各阶段孔隙均对总体积有一定贡献，而孔隙比表面积主要由微孔和介孔贡献。龙马溪组页岩孔隙符合分形规律，具有自相似性，宏孔孔隙结构较介孔、微孔更为复杂。以2个孔径段的孔体积比为加权值，计算获得综合分形维数为2.491～2.623，平均为2.560，孔隙结构较为复杂。有机碳含量和矿物组成对综合分形维数具有明显控制作用，有机碳含量越高，综合分形维数越大。孔隙结构复杂程度与综合分形维数呈正相关关系，脆性矿物含量与综合分形维数呈负相关关系，有机质成熟度和黏土矿物对孔隙综合分形维数有积极影响。

Pore structure and fractal characteristics of Longmaxi shale in southern Sichuan Basin

The pore development characteristics of Longmaxi shale in the southern Sichuan Basin have influence on shale gas occurrence and flow process. To scientifically evaluate the influence,the high-pressure mercury intrusion,low-temperature nitrogen and carbon dioxide adsorption were comprehensively used to characterize the pore structure,and the fractal fitting of pores in different size was made to calculate the integrated fractal dimensions,and combined with geochemistry and mineral composition,the influencing factors of the integrated fractal dimensions were discussed. The results indicate that the pore diameter distributions of the samples are multi-modal. The pores in different stages account for the pore volume to some extent,whereas micropores and mesopores account for the pore specific surface area. The pores of Longmaxi shale have self-similarity according with fractals laws,and compared with mesopores and micropores,the structure of macropore is more complex. Considering the pore volume of different pore diameters as the weighted value,the calculated integrated fractal dimensions are from 2.491 to 2.623,with an average of 2.560. The organic carbon content and mineral composition have an obvious controlling effect on the integrated fractal dimension which becomes larger with higher organic carbon content and more complex pore structure. The brittle mineral content is negatively correlated with the integrated fractal dimension,while the maturity and clay minerals have a positive influence on it.