Study on the Pore Structure Characteristics of Shale by Atomic Force Microscope and Energy Spectrum-Scanning Electron Microscope
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摘要: 已有研究表明页岩中纳米孔隙与组成导电膜的金颗粒处在同一量级，使得页岩中纳米孔隙在一定程度上被金颗粒掩埋，导致页岩中纳米孔隙被“二次改造”，从而无法真实观察到页岩中孔隙的形态特征；其次，由于受仪器分辨率、景深等因素的制约，无法观察到孔隙的三维展布特征。因此，如何真实地揭示纳米孔隙的空间结构特征，以及如何有效避免金颗粒对页岩储层中纳米孔隙的“二次改造”一直是微区分析的难点。本文通过扫描电镜（SEM）与原子力显微镜（AFM）方法组合观察到四川盆地龙马溪组黑色页岩中有机孔与无机孔在二维平面的分布存在较强的非均值性，孔径与孔隙的空间延展性呈现明显的正相关关系。有机孔呈蜂窝状分布，孔径主要分布在微米量级0.1~0.4μm，孔隙在三维空间呈现明显的“一体化”特征，具有较好的空间连通性；无机孔主要发育黏土矿物的层间孔隙，孔径主要分布在纳米量级16~57nm，此外见少量的矿物粒内不规则状溶蚀孔。研究认为，页岩中孔隙在二维平面的非均值性导致孔隙、喉道的分布会发生突变，从而影响储层的储集性能；页岩中孔隙在三维空间的非均值性导致页岩储层的渗透率在纵向上出现较大的差异，从而影响储层的物性特征。Abstract:
BACKGROUNDStudies have shown that the nano-pores in shale are at the same magnitude as the gold particles that make up the conductive film, and thus the pore size of nano-pores is blocked and buried by gold particles. The planar morphological characteristics of nano-pores cannot be observed due to the 'secondary transformation' of pores. Moreover, limited by the resolution and depth of field of the instrument, the spatial ductility and other structural characteristics of nano-pores cannot be observed. Therefore, how to truly reveal the spatial structure characteristics of nano-pores and how to effectively avoid the 'secondary modification' of nano-pores in shale reservoirs by gold particles has always been a difficulty in microanalysis. OBJECTIVESTo characterize the two/three dimensional structural characteristics of nano-pores in shale. METHODSAtomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to observe the pore features. RESULTSThe distribution of organic and inorganic pores in the black shale of the Longmaxi Formation in the Sichuan Basin has strong non-meanness, and the pore size and spatial ductility of the pores were significantly positively correlated. The organic pores were distributed in a honeycomb shape, with the pore size from 0.1 to 0.4μm. The pores show an obvious 'integrated' feature in the three-dimensional space and have good spatial connectivity. Inorganic pores mainly develop interlayer pores of clay minerals, and the pore size was mainly distributed between 16 and 57nm. In addition, there were a few irregular dissolution pores in mineral grains. CONCLUSIONSThe non-meanness of pores in the 2D plane of shale leads to abrupt changes in the distribution of pores and throats, which affects the reservoir performance. The non-meanness of pores in shale in three-dimensional space leads to the great difference of permeability of shale reservoir in the longitudinal direction, which affects the physical characteristics of the reservoir. -
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表 1 原子力显微镜参数
Table 1. Parameters of atomic force microscope
扫描模式 接触模式 扫描频率
(Hz)扫描范围 Z Gain SetPoint 成像信号 快速扫描 非接触模式
(NCM)0.5 20μm×20μm 1.5 20nm Z Height 精细扫描 轻敲模式
(Taping)0.4 5μm×5μm 2 15nm Z Drive 
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