Quantitative Characterization of Shale Pore Structure Based on Ar-SEM and PCAS
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摘要: 页岩孔隙特征是页岩储层研究的重要内容.基于沁水盆地S-1井太原组、山西组页岩样品,利用氩离子抛光扫描电镜(argon ion polishing scanning electron microscope,Ar-SEM)对孔隙形态特征进行分析,并运用孔裂隙特征分析系统软件(pores and cracks analysis system,PCAS)对Ar-SEM照片中孔隙进行定量表征.结果显示样品孔隙以有机质孔、粒间孔、粒内孔为主,孔径多集中在 < 100 nm,占比72.70%~82.13%,其中介孔占比39.76%~45.48%.随深度的增加孔隙结构越来越复杂,且越深的层位,随孔隙面积的增大其结构复杂程度增加的越缓慢.孔隙结构复杂程度在Ro,max=2附近存在拐点,高成熟阶段,随成熟度的增加孔隙结构复杂程度越来越低,且孔隙面积越大其结构复杂程度越低;过成熟阶段,随成熟度的增加孔隙结构复杂程度越来越高,且孔隙面积越大其结构复杂程度越高.Abstract: Shale pore characteristics are important part of shale reservoir research. Based on the shale samples from Taiyuan Formation and Shanxi Formation in the S-1 well of Qinshui basin, the morphology of the pores was analyzed by argon ion polishing scanning electron microscope (Ar-SEM), and the pores of the Ar-SEM micrographs were quantitatively characterized by pores and cracks analysis system (PCAS). The results show that the pore types of the samples are mainly organic matter pores, intergranular pores, and intragranular pores. The pore sizes are mostly less than 100 nm, accounting for 72.70%-82.13%, and the mesopore ratios are 39.76%-45.48%, which is favorable for pore connectivity and gas migration. The pore structure becomes increasingly more complex with the increase of depth; but the deeper the layer, the more slowly the structural complexity increases with the increase of pore area.There is an inflection point in the vicinity of Ro, max=2 for the pore structure complexity. In the high maturity stage, the complexity of the pore structure gets increasingly lower with the increase of the maturity, and the structure complexity is lower as the pore area is larger; in the over mature stage, pore structure is increasingly more complex with the increase of maturity, and the larger the pore area, the greater the structural complexity.
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表 1 基于PCAS获取的孔隙相关参数
Table 1. Parameters of pores obtained by PCAS
参数 SF-1 SF-2 SF-3 SF-4 SF-5 SF-6 SF-7 总孔数 696 442 432 325 367 337 491 孔隙度(%) 3.88 3.76 2.37 1.34 2.09 2.29 4.25 最大孔面积(μm2) 0.42 1.38 0.75 0.33 1.21 1.46 2.39 平均孔面积(μm2) 0.017 0.026 0.017 0.013 0.018 0.021 0.024 平均周长(nm) 608.79 704.64 628.01 523.46 597.04 658.84 687.69 形状因子 0.45 0.41 0.41 0.43 0.41 0.37 0.36 最大孔长(nm) 2 238.84 2 167.59 4 202.38 1 271.35 2 585.43 2 232.72 3 397.72 平均孔长(nm) 223.73 243.25 233.68 173.25 189.41 201.79 217.71 最大孔径(nm) 684.33 1 458.67 523.65 742.33 772.48 1 342.65 1 712.91 平均孔径(nm) 85.59 89.98 78.54 81.88 84.60 94.67 87.80 概率熵 0.85 0.81 0.8 0.73 0.77 0.73 0.76 分形维数 1.19 1.19 1.18 1.12 1.18 1.12 1.14 -
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