加载煤样各向异性超声响应特征研究

发布时间：2018-05-19 06:40

本文选题：原生结构煤 + 超声　；参考：《河南理工大学》2016年硕士论文

【摘要】：地球物理勘探技术是煤矿安全和煤层气开发的保障,开展加载条件下煤的超声实验为利用声波测井技术测定煤岩结构和物质组成提供理论和实验基础。本论文以研究原生结构煤在加载条件下的超声波-应变响应特征为目的,通过对平煤八矿不同变质程度、不同割理方向的煤样进行常温单轴加载条件下的超声波-应变测试实验,分析其弹性、应变响应差异。研究表明:(1)在应力未加载时,三种煤样的纵横波速度以及衰减系数都存在差异性,一般情况下平行层理的两个方向和垂直层理的方向相差较大,且存在垂直层理的方向纵横波速最小,衰减系数值较小,说明垂直层理方向煤样中超声波衰减的最厉害。这与沿Z方向煤样的压实效应最大有关。(2)在加载状态下,Qs普遍比Qp大,说明实际煤层对纵波的吸收衰减作用大于横波。在煤层某些参数测试方面,选择横波作为检测波更有优势。煤样衰减各向异性系数大于速度各向异性系数,这也说明了品质因子Q可能是一个比速度对煤样各向异性更为敏感的参数。(3)两种焦煤随着应力的增加,平行层理的两个方向的纵横波速和衰减各向异性变化趋势都不尽相同,一般情况下Y方向纵横波速和衰减的各向异性系数都大于X方向。这也间接说明了煤层中裂隙的走向变异程度具有差异性。(4)加载过程中,煤样的V_p随着应力的升高而逐渐增加,但在低应力段的增长幅度要高于高应力区段。在0-2MPa低应力区间时,V_p的增大幅度较快,当应力高于2MPa时,V_p的增长幅度也开始变慢。针对三种煤样的V_S而言,其变化趋势和V_p类似,低应力区波速增长幅度较大,到达V_S最大值后迅速下降。此外,三种煤样抗压强度存在差异,同种变质程度煤样三个方向上也存在差异。V_S最大值点不同变质程度煤样出现在不同应力加载处。(5)对于加载状态下三种变质程度煤样来说,体积模量变化从整体上来说都是先增加后到达某个最大点或者时稳定在一段时间后下降,这个过程包含了煤样中孔隙的闭合、张开和发育等阶段;针对某种特定变质程度的煤样来说,在加载状态下,三种煤样的体积模量也是随着加载应力的增加而增大,但是三个方向上体积模量的增加快慢存在差异。一般情况下都是平行层理的两个方向的体积模量大于垂直层理方向。通过对单轴应力作用下同一矿区不同变质程度、不同割理方向的原生结构煤的超声波-应变响应特征进行分析,探索了同一矿区煤岩在宏观和微观物质组成、结构及构造在弹性特征和应变方面的差异,为今后运用地震勘探探测煤层物性、结构及软分层的分布提供理论及实验基础。
[Abstract]:Geophysical exploration technology is the guarantee of coal mine safety and coalbed methane development. The ultrasonic experiment of coal under loading condition provides a theoretical and experimental basis for the determination of coal structure and material composition by using acoustic logging technology. In order to study the ultrasonic and strain response characteristics of primary structure coal under loading conditions, the metamorphic degree of the coal under different metamorphic degrees is studied in this paper. The ultrasonic and strain tests of coal samples with different cleavage directions under uniaxial loading at room temperature were carried out to analyze the difference in elasticity and strain response. The results show that the longitudinal and shear wave velocities and attenuation coefficients of the three kinds of coal samples are different when the stress is not loaded. In general, the two directions of parallel bedding and the direction of vertical bedding are quite different. The longitudinal and transverse wave velocity in the direction of vertical bedding is the smallest and the attenuation coefficient is small, which indicates that the ultrasonic wave attenuation is the most severe in the coal samples in the vertical stratification direction. This is related to the maximum compaction effect of coal samples along Z direction. 2) under loading condition, Qs is generally larger than QP, indicating that the absorption and attenuation of longitudinal wave in actual coal seam is greater than that in S-wave. In some coal seam parameters test, it is more advantageous to select the shear wave as the detection wave. The attenuation anisotropy coefficient of coal sample is larger than that of velocity anisotropy coefficient, which indicates that the quality factor Q is a more sensitive parameter than velocity to the anisotropy of coal sample. The variation trends of longitudinal and transverse wave velocities and attenuation anisotropy in two directions of parallel layer are different. In general, the anisotropy coefficients of Y direction longitudinal and transverse wave velocity and attenuation are larger than X direction. This also indirectly shows that during the loading process, the VSP of coal samples increases with the increase of stress, but the increase of VSP in the low stress section is higher than that in the high stress zone. When the stress of 0-2MPa is higher than that of 2MPa, the increase of VSP increases rapidly, and the increase of VSP becomes slower when the stress is higher than that of 2MPa. For the three kinds of coal samples, the variation trend is similar to that of V\ +\ {\}\ In addition, the compressive strength of the three kinds of coal samples is different, and there are also differences in three directions of the same metamorphic coal samples. The maximum value of V _ S and different metamorphic coal samples appear at different stress loading sites. (5) for the three kinds of metamorphic coal samples under loading state, the three metamorphic coal samples have different degrees of metamorphism. As a whole, the volume modulus changes are first increased and then reached a certain maximum point, or stable after a period of time, which includes the stages of pore closure, opening and development in coal samples. For a coal sample with a specific metamorphic degree, the bulk modulus of the three coal samples increases with the increase of the loading stress under the loading condition, but the increase rate of the bulk modulus in the three directions is different. In general, the volume modulus in two directions of parallel bedding is larger than that in vertical direction. By analyzing the ultrasonic strain response characteristics of primary structural coal with different metamorphism degree and different cleat direction under uniaxial stress, the macroscopic and microscopic composition of coal and rock in the same mining area is explored. The differences in elastic characteristics and strain between structures and structures provide a theoretical and experimental basis for the future application of seismic exploration to detect the distribution of coal bed physical properties, structure and soft stratification.
【学位授予单位】：河南理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TD315

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