基于流体吸入实验的页岩纳米孔隙连通性分析方法

A method for analyzing nanopore connectivity of shale using a fluid suction experiment

张文涛 胡文瑄 鲍芳 俞凌杰 范明 张庆珍

ZHANG Wentao HU Wenxuan BAO Fang YU Lingjie FAN Ming ZHANG Qingzhen

南京大学 地球科学与工程学院 南京 210046 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126

School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210046, China Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China

提出了基于含示踪剂流体吸入实验的页岩连通性分析方法。通过真空吸入的方式使氯金酸钠溶液进入页岩孔隙中，并使之转化为固态金，将完成实验后的样品表面进行氩离子抛光处理，并在场发射扫描电镜下观察金的分布，可以获得页岩中连通孔隙在纳米尺度上的特征。根据四川盆地上奥陶统五峰组-下志留统龙马溪组2个岩心样品的实验结果，认为其连通网络可分为三级系统。有机质内部孔隙连通性与孔隙发育程度有关，喉道半径小，流动效率不高。粒缘缝主要分布在颗粒矿物边缘、有机质与矿物之间以及片状黏土矿物边缘，是流体流动的有利通道，有机质孔通过粒缘缝相互连通。微裂缝的发育能够很好地改善页岩孔隙的连通性，是流体流动的优势通道。页岩连通性具有各向异性，页岩孔隙在平行层理方向的连通性大大优于垂直层理方向。

A method for analyzing the pore connectivity of shale based on a suction experiment of tracer fluid is presented. Sodium chloraurate solution is absorbed into shale pores which have been previously evacuated, and then the solute in the pores is converted to gold by heating. After the suction experiment, the sample surface is polished and analyzed with scanning electron microscopy, in order to get the characteristics of connected pores at the nano-scale. The results of two core samples from the Wufeng-Longmaxi formations in the Sichuan Basin show the connected network in shale could be divided into three parts. The interior connectivity of pores in organic matter is related to the density of pores, and organic matter normally has low flow efficiency because of narrow throat radius. Fractures distributed at grain boundaries such as minerals, organic matter and clay sheets are advantageous pathways, and organic pores are connected by grain boundaries. The development of micro-cracks/fractures, which have high permeability, could significantly improve shale connectivity. Shale pore connectivity has great anisotropy, which means connectivity parallel to bedding is much better than that vertical to bedding.

国家自然科学基金 U1663202;国家自然科学基金 41690133;国家油气重大专项 2017ZX05036002

https://doi.org/10.11781/sysydz202003415