含氮气煤体超声各向异性特征实验研究

探讨含气煤体超声响应特征可为利用超声技术在煤岩物性特征测试中的应用提供依据。利用自主研发的煤储层物性特征实验系统，选取平煤八矿己_16-17煤层煤样，制备平行层理与面割理（x）、平行层理垂直面割理（y）和垂直层理（z）等3类煤样，对含氮气煤体在不同气体压力及不同吸附时间下的超声特征进行测试。实验结果表明：（1）轴压恒定时，随着围压增加，煤的弹性波速度不断增加，煤体抽真空状态下的纵、横波速度略大于常压下的波速；（2）煤柱从负压状态到注气吸附状态，随着注气时间的延长，波速先下降，然后缓慢升高；（3）轴压和围压不变时，随着气体压力的变化，纵波和横波速度均有所增加；（4）平行层理与面割理、平行层理垂直面割理和垂直层理方向各向异性明显，但超声响应规律基本一致；（5）煤样纵波和横波垂直、平行层理方向各向异性程度与吸附时间的关系差异明显，纵波各向异性程度对吸附时间更加敏感。

Experimental Study on Ultrasonic Anisotropic Characteristics of Nitrogen-containing Coal Bodies

The investigation of ultrasonic response characteristics of gas-bearing coal bodies can provide the basis for application of ultrasonic technologies for testing the physical properties of coal. An independently developed coal reservoir physical property experimental system was used. Coal samples were selected from the 16-17 Coal Seam of the Pingdingshan Eighth Mine to prepare three kinds of coal samples:the parallel bedding and surface cleat (x), parallel bedding and vertical surface cleat (y), and vertical bedding (z), in which the ultrasonic characteristics of nitrogen-containing coal bodies under different gas pressures and at different adsorption times were tested. The experimental results show that (1) when the axial pressure is constant, as the confining pressure increases, the elastic wave velocity of coal increases continuously, and the P-and S-wave velocity of the coal in a vacuum is slightly greater than that under normal pressure; (2) from the negative pressure state to the gas injection and adsorption state, the velocity of the coal column first decreases and then slowly increases with the extension of the gas injection duration; (3) when the axial pressure and confining pressure are constant, the P-and S-wave velocity increases with the change of gas pressure; (4) the anisotropy among the parallel bedding and surface cleat, parallel bedding and vertical surface cleat, and direction of the vertical bedding is significant, but the ultrasonic response patterns are basically the same; and (5) the relationship between the anisotropy degree of the vertical and parallel bedding and the adsorption time is significantly different between the P-and S-waves of the coal samples. The anisotropy degree of the P-wave is more sensitive to the adsorption time.