基于分形理论的页岩纳米孔隙粒度效应探究

Study on the particle size effect of shale nanopore based on fractal theory

秦钰佳 唐鑫 程龙飞 周廷强 向磊 郭森

重庆三峡学院土木工程学院，重庆 404199 重庆市三峡水库岸坡与工程结构灾变防控工程技术研究中心，重庆 404199 三峡库区水环境演变与污染防治重庆市重点实验室，重庆 404020 中国矿业大学煤层气与成藏过程教育部重点实验室，江苏 徐州 221008

College of Civil Engineering, Chongqing Three Gorges University, Chongqing 404199, China Chongqing Three Gorges Reservoir Bank Slope and Engineering Structure Disaster Prevention and Control Engineering Technology Research Center, Chongqing 404199, China Chongqing Key Laboratory of Water Environment Evolution and Pollution Control in Three Gorges Reservoir Area, Chongqing 404020, China MOE Key Laboratory of Coalbed Methane and Reservoir Forming Process, China University of Mining and Technology, Xuzhou 221008, China

为了研究低温液氮吸附实验中样品粒径对页岩孔隙结构特征的影响，文中以贵州南部三都水族自治县北部的牛蹄塘组页岩为例，通过物理破碎获得不同粒径的页岩样品，分别对破碎后6组不同粒径的页岩样品开展了常规物性实验，并将破碎筛分后的样品进行了扫描电镜观测实验，同时基于分形维数理论，探索破碎筛分后纳米孔隙的粒度效应及分维特征，并从微观孔隙变化特征揭示了孔隙影响机理。结果表明：破碎筛分后的样品中，粒径小于74 μm的样品孔隙体积与其余粒径的样品相差很大，并且孔径达到14.359 nm，表明过度的破碎筛分会使实验结果产生误差；粒径96~120 μm的样品孔隙体积比120~150 μm的大，表明页岩在研磨破碎过程中，部分封闭的有机质孔可能会变为开放孔，同时也可能会在有机质中形成一些新的人工微裂缝，进而增加页岩的孔隙体积。综合实验数据的可靠性及时效性等因素，建议采用120~180 μm的样品来开展研究区页岩的孔径参数分析测试实验。

In order to study the influence of different particle sizes on the pore structure characteristics of shale in low-temperature nitrogen adsorption experiments, taking the shale of Niutitang Formation in the north of Sandu Shui Autonomous County in southern Guizhou as an example in this paper, the conventional physical properties of six groups of shale samples with different particle sizes after crushing were respectively carried out by deffrent size of physically crushed shale samples, and the samples after crushing and screening were observed by scanning electron microscopy. At the same time, based on the fractal dimension theory, the particle size effect and fractal dimension characteristics of nanopore after crushing and screening were explored, and the influencing mechanism on the pore was revealed from the variation characteristics of microscopic pore. The results show that in the sample after crushing and screening, the pore volume less than 74 μm is very different from the rest of shale particle size and the pore size reaches 14.359 nm, which indicates that excessive crushing and screening will cause error to the experimental results. The pore volume of 96-120 μm is larger than that of 120-150 μm, which indicates that during the grinding and crushing process of shale, some closed organic pores may become open pores, and some new artificial  microcracks may be formed in organic matter, thereby increasing the total pore volume of shale. Based on the reliability and timeliness of experimental data, it is suggested to use 80-120 μm samples to carry out the analysis and test of shale pore size parameter.

10.6056/dkyqt202204014