地球物理学报 ›› 2016, Vol. 59 ›› Issue (10): 3891–3900.doi: 10.6038/cjg20161032

• 应用地球物理学 • 上一篇    下一篇

涪陵地区井下页岩岩芯裂缝体密度与声学性质关系实验研究

伍宇明1,3, 兰恒星1, 高星1, 王伟1, 陈俊辉1,3, 郝召兵2   

  1. 1 中国科学院地理科学与资源研究所, 北京 100101;
    2 中国科学院地质与地球物理研究所, 北京 100029;
    3 中国科学院大学, 北京 100049
  • 收稿日期:2016-01-04 修回日期:2016-09-08 出版日期:2016-10-05
  • 通讯作者: 王伟,男,1972年生,助理研究员,从事地球物理方面研究.E-mail:wang_wei@lreis.ac.cn E-mail:wang_wei@lreis.ac.cn
  • 作者简介:伍宇明,男,1989年生,在读博士,从事页岩气和灾害方面研究.E-mail:wuym@lreis.ac.cn
  • 基金资助:
    中国科学院战略性先导科技专项(B类)(XDB10030300),国家自然科学基金(41525010、41204096和41374061)资助.

The relationship between the volume density of cracks and acoustic properties of the shale core samples from Fulin

WU Yu-Ming1,3, LAN Heng-Xing1, GAO Xing1, WANG Wei1, CHEN Jun-Hui1,3, HAO Zhao-Bing2   

  1. 1 Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;
    2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;
    3 University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2016-01-04 Revised:2016-09-08 Online:2016-10-05

摘要: 本研究对涪陵地区井下产气的龙马溪组页岩岩芯,采用三轴压机压裂制造裂缝,用工业CT扫描压裂前后岩芯,应用图像识别技术统计出裂缝体密度,又用超声脉冲透射法测定样品破裂前后裂缝方向上的纵波、单偏振方向与裂缝不同夹角的横波,来研究裂缝对页岩岩芯声学性质的影响.实验结果表明:压裂后样品的纵波速度略微降低,只有含较多内部裂隙的150#样品纵波速度减小幅度明显.压裂前后样品的纵波波形差别不大,纵波主频随裂缝体密度呈下降趋势,即压裂后纵波频谱主频向低频端移动.压裂前横波速度随自身与裂隙方位角变化而变化,与0°和180°相比,在45°和135°时略微减小,在90°时速度降低幅度最为明显并且发生相位反转.典型样品的横波主频随偏振方向与裂缝夹角的增大而逐渐向低频移动;压裂后,横波频谱杂乱,出现多处局部峰值,速度和主频较压裂前更低,平均横波波速随裂缝体密度呈明显减小趋势.平均纵横波速比随裂缝密度呈近线性增加,表明其与裂缝体密度有较强相关性.

关键词: 页岩, 声波, 裂缝体密度, CT扫描

Abstract: This article discusses the elastic wave velocity and frequency spectrum of the Longmaxi Shale from Fulin, Chongqing, China. The TAW-2000 Rock Tri-axial Testing System was applied on the core samples to produce fractures with different distributions. The distributions of fractures before and after the cracking test were obtained by X-CT. The volume density of cracks was obtained by computer pattern recognition. Accordingly, the relationship between the compression wave and the single-polarization shear wave in different angles with the crack and different distributions of cracks was investigated in a lab environment. The experimental results show that, the velocity of compression wave in fractured samples is slightly lower than that of original samples, except for the 150# sample. The waveforms of compression wave before and after the compression are similar, but the dominant frequency of the waveform of compression wave becomes lower after fracturing. The wave velocity of the shear wave varies with the azimuthal angle between the vibration direction and the fracture direction. The velocity reaches the highest and lowest values when the S-wave polarization is parallel and perpendicular to the strike direction of fracture, respectively. The velocity is moderate in diagonal directions. If the vibration direction is perpendicular to the fracture plane, the shear wave is opposite to the original direction. Specifically, before the compression, the dominant frequency of shear wave for typical samples decreases with the azimuthal angle, while after the compression, in contrast, the dominant frequency is crashed and many local peaks arise in the spectrum, especially at lower frequency band. The average velocity of shear wave decreases as the volume of density of cracks increases. In addition, the average wave velocity ratio between shear wave and compressional wave has a strong relationship with the volume density of cracks. Therefore, our experiments show that the shear wave is more sensitive to the fractures compared with the compressional wave, and indicate that shear wave exploration is more effective for detecting targets that have many fractures.

Key words: Shales, Ultrasonic wave, Volume density of cracks, CT scan

中图分类号: 

  • P631
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