天然气地球科学 ›› 2020, Vol. 31 ›› Issue (1): 84–92.doi: 10.11764/j.issn.1672-1926.2019.10.006

• 非常规天然气 • 上一篇    下一篇

高阶煤的孔隙结构特征及其对煤层气解吸的影响

许耀波1,2(),朱玉双1()   

  1. 1.西北大学大陆动力学国家重点实验室/西北大学地质学系,陕西 西安 710069
    2.中国煤科工集团西安研究院有限公司,陕西 西安 710054
  • 收稿日期:2019-05-29 修回日期:2019-10-06 出版日期:2020-01-10 发布日期:2019-11-06
  • 通讯作者: 朱玉双 E-mail:xuyaobo@cctegxian.com;yshzhu@nwu.edu.cn
  • 作者简介:许耀波(1983-),男,湖南衡阳人,副研究员,主要从事煤层气开发研究.E-mail: xuyaobo@cctegxian.com.
  • 基金资助:
    国家自然科学基金(51874349);中国煤炭科工集团科技创新创业资金项目(2018MS008)

Pore structure characteristics of high rank coal and its effect on CBM desorption

Yao-bo XU1,2(),Yu-shuang ZHU1()   

  1. 1.State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China
    2.Xi’an Research Institute of China Coal Technology & Engineering Group Corp, Xi’an 710054,China
  • Received:2019-05-29 Revised:2019-10-06 Online:2020-01-10 Published:2019-11-06
  • Contact: Yu-shuang ZHU E-mail:xuyaobo@cctegxian.com;yshzhu@nwu.edu.cn
  • Supported by:
    National Natural Science Foundation of China(51874349);China Coal Technology & Engineering Group Technology Innovation Project(2018MS008)

摘要:

以沁水盆地高阶煤3#煤层为研究对象,借助高压压汞实验对高阶煤的孔隙参数进行测试,研究了高阶煤的孔隙结构特征,采用解吸速率实验对高阶煤的解吸速率和解吸量进行分析,并探讨了孔隙结构对煤层气解吸产出的控制规律。结果表明:3#煤层的孔隙半径较小,煤层孔隙结构复杂;煤层主要以气体吸附孔和气体扩散孔为主,气体渗流孔占比很少,煤层的吸附气体体积大、吸附性能强、气体的扩散、渗流条件差。3#煤层孔隙结构分形特征曲线呈“两段型”,孔径大于940.7 nm时,不具有分形特征;孔径小于940.7 nm时,分形维数介于2.67~2.76之间,具有很好的分形特征。高阶煤的煤层气解吸特征具有快速解吸和慢速解吸2个阶段,快速解吸时间短,解吸量占比低;慢速解吸时间长,解吸量占比高,煤层气解吸困难。煤层的孔隙结构对煤层气的解吸具有重要影响,高阶煤较差的孔隙结构控制着煤层气解吸速率慢、解吸量低、产出程度低,煤层气井生产实践中表现为开始阶段产气量增长快,产气高峰时间短,稳产气量低、生产时间长,煤层气开发难度大。研究结果为高阶煤的煤层气抽采效果评价提供参考依据。

关键词: 高阶煤, 煤层气, 孔隙结构, 分形特征, 高压压汞, 解吸速率, 控制规律

Abstract:

Taking No.3 coal of high-rank coal in Qinshui Basin as a research object, the pore structure characteristics of high-rank coal were analyzed by high-pressure mercury injection experiment, and the desorption rate experiment was used to analyze the desorption characteristics of high-rank coal, and the control law of pore structure on CBM desorption was studied. The results show that: The pore radius of the No.3 coal seam is small and the pore structure of the coal seam is complex. The coal seam is mainly dominated by gas adsorption pore and gas diffusion pore, and the gas seepage pore accounts for a small proportion. The No.3 coal is large in volume of adsorption gas, strong in adsorption performance, poor in gas diffusion and seepage conditions. The fractal characteristic curve of the pore structure of No.3 coal seam shows a "two-section type". When the pore diameter is bigger than 940.7nm, it has no fractal characteristic. When the aperture is smaller than 940.7nm, the fractal dimension is between 2.67 and 2.76, with good fractal characteristics. The desorption of CBM in high-rank coal with rapid desorption and slow desorption has two distinct stages. Rapid desorption time is short, desorption rate is low, slow desorption time is long, desorption rate is high, and CBM desorption is very difficult. The pore structure of high rank coal controls the output of CBM. The poor pore structure of high rank coal results in low degree of CBM output and slow desorption rate. In the practice of CBM well drainage and gas recovery, it is difficult to develop CBM due to the rapid growth of gas production in the initial stage, short stable period of peak gas production, low gas production and long production time. The results provide a reference for evaluation of CBM extraction efficiency of high rank coal.

Key words: Higher rank coal, Coalbed methane, Pore structure, Fractal characteristics, High pressure mercury injection, Desorption rate, Control law

中图分类号: 

  • TE122.2+3

图1

赵庄井田区域位置与含煤地层柱状图"

表1

煤心孔隙度和渗透率测试数据"

煤心编号煤心长度/cm煤心直径/cm密度/(g/cm3孔隙体积/cm3孔隙度/%水平渗透率/(10-3 μm2)
No.12.2802.6101.0141.1589.500.83
No.22.3382.6161.0321.27610.213.16
No.32.2802.6100.9651.0688.741.35
No.42.3482.6321.0761.2309.790.32

图2

3#煤高压压汞毛管压力曲线与毛管半径分布特征(a)、(b)为No.1号样品;(c)、(d)为No.2号样品;(e)、(f)为No.3号样品;(g)、(h)为No.4号样品"

表2

煤岩的孔喉半径分布数据"

煤样孔喉半径比例/%
r>1.00.1<r≤1.00.01<r≤0.1r≤0.01
No.11.284.3737.1657.19
No.21.417.2238.3353.04
No.30.748.7437.6752.85
No.41.656.1439.7852.43

图3

3#煤压汞孔隙半径分布"

图4

煤岩的孔隙结构分形特征"

表3

煤岩的孔隙结构分形拟合数据表"

煤样孔隙度/%渗透率/(10-3 μm2孔径范围/nm拟合方程分形维数(D)拟合度(R2)
No.19.500.83>940.7y=2.593 6x+0.701 4D1:4.590.971
3.6~940.7y=0.711 2x+0.252 6D2:2.710.983
No.210.213.16>940.7y=2.351 7x+0.683 8D1:4.350.982
3.6~940.7y=0.678 1x+0.389 6D2:2.670.998
No.38.741.35>940.7y=2.266 1x+0.314 4D1:4.260.972
3.6~940.7y=0.766 7x+0.260 8D2:2.760.982
No.49.790.32>940.7y=2.528 4x+0.800 6D1:4.520.968
3.6~940.7y=0.685 2x+0.376 7D2:2.680.996

图5

分形维数与孔隙度和渗透率的关系"

图6

煤层气解吸速率曲线"

图7

不同解吸速率下的解吸量对比"

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