天然气地球科学 ›› 2020, Vol. 31 ›› Issue (7): 1028–1040.doi: 10.11764/j.issn.1672-1926.2020.03.013

• 非常规天然气 • 上一篇    下一篇

基于低温CO2吸附的煤和页岩微孔结构分形分析

熊益华1(),周尚文2,焦鹏飞2,杨明伟2,周军平3,韦伟1,蔡建超1()   

  1. 1.中国地质大学地球物理与空间信息学院,湖北 武汉 430074
    2.中国石油勘探开发研究院,北京 100083
    3.重庆大学煤矿灾害动力学与控制国家重点实验室,重庆 400044
  • 收稿日期:2019-12-28 修回日期:2020-03-29 出版日期:2020-07-10 发布日期:2020-07-02
  • 通讯作者: 蔡建超 E-mail:lingkongdaxia@163.com;caijc@cug.edu.cn
  • 作者简介:熊益华(1995-),男,四川自贡人,硕士研究生,主要从事煤和页岩微观孔隙结构表征研究.E-mail:lingkongdaxia@163.com.
  • 基金资助:
    国家科技重大专项(2017ZX05035002-002);国家自然科学基金(41722403)

Fractal analysis of micropore structures in coal and shale based on low-temperature CO2 adsorption

Yi-hua XIONG1(),Shang-wen ZHOU2,Peng-fei JIAO2,Ming-wei YANG2,Jun-ping ZHOU3,Wei WEI1,Jian-chao CAI1()   

  1. 1.Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China
    2.PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China
    3.The State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
  • Received:2019-12-28 Revised:2020-03-29 Online:2020-07-10 Published:2020-07-02
  • Contact: Jian-chao CAI E-mail:lingkongdaxia@163.com;caijc@cug.edu.cn
  • Supported by:
    The China National Science and Technology Major Projects(2017ZX05035002-002);The Natural Science Foundation of China(41722403)

摘要:

分形维数是分析煤和页岩微观孔隙结构的重要参数之一。目前主要是基于低温N2吸附数据进而利用Frenkel?Halsey?Hill(FHH)模型,获得煤和页岩中孔(2~50 nm)与宏孔(>50 nm)的表面粗糙分形维数,对其微孔(<2 nm)分形维数的研究还较少。为深入研究煤和页岩的微孔特征,基于微孔填充与孔径分布理论,对比分析了煤和页岩微孔结构的分形特征。选取煤和页岩样品进行低温CO2吸附实验,计算并分析两者的微孔分形维数。结果表明:煤的微孔分形维数分布在2.6~2.8之间,平均为2.75;页岩的微孔分形维数分布在2.8~2.9之间,平均为2.88。煤的微孔比表面积分布在100~300 m2/g之间;页岩的微孔比表面积集中在15~30 m2/g之间,页岩的孔隙分布零散且数量少,说明分形维数越大,微孔结构更加复杂。此外,分别对煤与页岩的微孔分形维数、表面粗糙分形维数进行了对比,发现虽然煤的微孔比表面积均远大于页岩,但其孔径分布、孔隙结构比页岩简单,微孔分形维数小于页岩。同时,由于中孔、宏孔数量少,比表面积小,孔隙表面较为光滑,煤的表面粗糙分形维数小于页岩。微孔分形维数和表面粗糙分形维数分别受微孔结构复杂程度与中孔、宏孔表面粗糙程度的影响,微孔结构越复杂,中孔、宏孔表面越粗糙,分形维数越大。

关键词: 微孔分形维数, FHH模型, 低温CO2吸附, 低温N2吸附

Abstract:

An effective method to accurately characterize and quantify the pore structure of coal and shale is a key issue. At present, the fractal dimension of surface roughness (D2) of coal and shale is mainly analyzed based on the low-temperature nitrogen adsorption experiments and Frenkel-Halsey-Hill (FHH) model, but the micropore fractal dimension (Dm) is still rarely studied. This paper based on the micropore-filling theory and micropore-aperture distribution theory, a Dm model of coal and shale was proposed. The low-temperature CO2 adsorption experiments were done, and the fractal analysis of CO2 adsorption isotherms corresponding to coal and shale samples were carried out by using the Dm method. The results show that the Dm of coal is ranging from 2.6 to 2.8, with an average of 2.75, while that of shale ranges from 2.8 to 2.9, with an average of 2.88. The specific surface area of micropore of shale is ranging from 15 m2/g to 30 m2/g, while the specific surface area of micropore of coal is ranging from 100 m2/g to 300 m2/g. It shows that the pore distribution of shale is scattered and the number of pore is small, indicating that shale has a more complicated and heterogeneous micropore structure. The Dm and D2 are compared. The pore volume and specific surface area of micropore of coal are much larger than that of macropores, and the micropore structure is more complex. Meanwhile, the small number of mesopores and macropores, small specific surface area and smooth pore surface, make Dm of coal larger than D2. Dm and D2 are respectively affected by the complexity of microporous structure and the roughness of mesopore and macropore surface. Complex micropore structure and rough pore surface will increase the fractal dimension.

Key words: Micropore fractal dimension, FHH model, Low-temperature CO2 adsorption, Low-temperature N2 adsorption

中图分类号: 

  • TE151

表 1

页岩样品岩石物理信息"

样品 编号层位黏土矿物 含量/%脆性矿物 含量/%

TOC

/%

核磁孔隙度

/%

Y-1龙马溪组22.561.40.88.58
Y-2龙马溪组27.949.30.78.00
Y-3龙马溪组17.746.93.23.71
Y-4龙马溪组24.744.61.97.28
Y-5龙马溪组20.343.71.710.27
Y-6龙马溪组14.447.41.76.45
Y-7五峰组3.327.22.05.98
Y-8五峰组16.520.74.62.71
Y-9五峰组38.042.94.88.07

表 2

煤样品岩石物理信息"

样品编号层位总有机质含量/%镜质组含量/%RO/%氦测孔隙度/%渗透率/(10-3 μm2
M-1山西组81.671.91.41.70.002 7
M-2山西组76.782.31.45.60.329 3
M-3太原组83.486.01.51.30.105 0
M-4本溪组84.291.41.51.30.005 3
M-5本溪组76.683.71.72.40.001 1
M-6本溪组77.979.21.71.20.155 1
M-7本溪组80.587.21.81.4-

图1

煤(a)和页岩(b)样品CO2吸附解吸曲线"

图2

煤(a,b)与页岩(c,d)的DFT孔径分布曲线"

图3

煤与页岩微孔孔隙体积比较"

表3

煤、页岩样品ρ、v参数拟合结果"

样品编号ρ/(kJ·mol)v样品编号ρ/(kJ·mol)v
M-113.002.05Y-114.632.03
M-213.162.05Y-214.811.98
M-313.332.08Y-315.052.02
M-413.222.09Y-415.132.08
M-512.921.99Y-515.022.00
M-610.362.08Y-614.982.05
M-79.552.10Y-715.042.03
Y-815.872.09
Y-915.031.98

图4

煤(a)和页岩(b)样品J(x)和x双对数曲线"

表4

煤、页岩样品微孔分形维数模型拟合公式与相关系数"

样品编号拟合公式R2样品编号拟合公式R2
M-1y=-0.781 3x-1.172 40.988 3Y-1y=-0.850 6x-1.060 60.995 6
M-2y=-0.789 3x-1.160 40.988 7Y-2y=-0.882 4x-1.070 70.995 9
M-3y=-0.784 8x-1.141 70.988 8Y-3y=-0.881 6x-1.050 60.996 1
M-4y=-0.775 9x-1.148 60.988 5Y-4y=-0.858 5x-1.026 60.996 1
M-5y=-0.804 9x-1.191 70.988 6Y-5y=-0.888 4x-1.058 60.996 1
M-6y=-0.663 7x-1.466 80.981 3Y-6y=-0.860 5x-1.039 50.995 9
M-7y=-0.629 2x-1.598 50.978 8Y-7y=-0.874 8x-1.046 30.996 1
Y-8y=-0.908 6x-1.010 30.996 9
Y-9y=-0.897 2x-1.065 00.996 1

表5

煤和页岩样品微孔分形维数计算结果"

样品编号V0 /(cm3/g )比表面积/(m2/g)Dm样品编号V0 /(cm3/g )比表面积/(m2/g)Dm
M-121.95100.232.78Y-14.7821.852.85
M-223.77108.552.79Y-24.1218.802.88
M-337.82172.672.78Y-32.7012.322.88
M-436.93168.642.78Y-43.5015.972.86
M-532.20147.022.80Y-53.3715.392.89
M-660.14274.592.66Y-63.6016.432.86
M-764.48294.442.63Y-73.2614.862.87
Y-81.707.782.91
Y-94.3619.932.90

图5

煤(a)与页岩(b)样品低温N2吸附解吸曲线(实心点为吸附点、空心点为解吸点)"

图6

煤与页岩N2吸附孔隙体积对比"

图7

利用FHH模型拟合煤(a)与页岩(b)吸附数据"

表6

煤、页岩样品FHH拟合公式与相关系数"

样品编号D1D2
拟合公式R2拟合公式R2
M-1y=-0.480 1x-1.341 40.967 7y=-0.449 3x-1.458 60.997 6
M-2y=-0.459 5x-1.793 40.941 5y=-0.321 5x-1.793 20.994 3
M-3y=-0.165 4x-2.500 80.606 3y=-0.504 1x-2.832 50.997 3
M-4y=-0.095 0x-2.446 60.213 9y=-0.511 6x-2.936 60.993 8
M-5y=-0.350 7x-1.493 30.925 5y=-0.505 8x-1.703 40.995 3
M-6y=0.061 7x-2.321 50.146 9y=-0.675 8x-2.988 90.986 0
M-7y=-0.454 7x-1.615 50.947 0y=-0.455 3x-1.785 10.989 4
Y-1y=-0.332 3x+1.942 00.991 1y=-0.265 2x+1.934 60.998 9
Y-2y=-0.346 2x+1.850 30.994 4y=-0.282 5x+1.847 50.998 8
Y-3y=-0.326 0x+2.258 10.993 5y=-0.285 8x+2.255 00.998 5
Y-4y=-0.330 7x+1.993 10.991 8y=-0.251 9x+1.997 90.997 6
Y-5y=-0.334 4x+2.019 00.991 7y=-0.254 5x+2.031 70.996 7
Y-6y=-0.310 4x+1.830 10.982 6y=-0.212 0x+1.867 60.980 7
Y-7y=-0.303 1x+2.485 90.982 7y=-0.194 9x+2.518 80.989 3
Y-8y=-0.328 3x+2.358 30.993 0y=-0.215 1x+2.374 60.999 6
Y-9y=-0.304 7x+1.969 50.983 8y=-0.209 8x+1.999 00.989 8

表7

煤与页岩表面粗糙分形维数计算结果"

样品编号V0/(m3/g)比表面积/(m2/g)D1D2
M-10.180.792.522.55
M-20.120.512.542.68
M-30.060.262.832.50
M-40.070.282.902.49
M-50.160.702.652.49
M-60.070.323.062.32
M-70.140.612.552.54
Y-14.6820.392.712.74
Y-24.2618.522.692.72
Y-36.4327.992.712.75
Y-44.9321.462.712.76
Y-55.0522.002.702.76
Y-64.2118.322.732.82
Y-78.1235.362.742.83
Y-87.1230.982.722.79
Y-94.8421.082.732.81

图8

煤(a)、页岩(b)孔隙体积与比表面积对比"

图9

煤与页岩分形维数与比表面积关系[(a)、(c):煤;(b)、(d):页岩]"

图10

煤与页岩分形维数与孔隙体积关系[(a)、(c):煤;(b)、(d):页岩]"

图11

煤与页岩微孔分形维数对比"

图12

煤和页岩表面粗糙分形维数D2对比"

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