矿井含水构造瞬变电磁场响应及透视技术研究

发布时间：2018-05-10 05:48

本文选题：全空间响应 + 磁偶极子源　；参考：《中国矿业大学》2017年博士论文

【摘要】：矿井瞬变电磁法是构建煤矿突水危险源预测预报多方法、多阶段、井上下立体综合预警模式的重要勘察手段之一。该方法具有效率高、对良导含水构造灵敏的优点。但与地面瞬变电磁法相比,该方法在理论上还未完全搞清,尚存在很多亟待解决的问题,如计算视电阻率偏小、地电异常体的空间定位和定向探测问题、有效探测深度和时深转换等问题。本文针对地电体空间定位和定向探测问题,采用数值模拟方法对全空间地电异常体的响应特征进行了研究,并探索了一种新的探测方式。论文在前人的研究基础上,从三维电场扩散方程出发,基于正交六面体剖分推导了有限体积法(广义差分法)的无条件稳定的Du Fort-Frankel差分格式,避免了从磁场扩散方程构造的差分格式中需要计算电导率导数问题。采用均匀全空间磁偶源电场的解析解作为初始条件代入源;在大的求解区域条件下,采用非均匀网格空间离散方式不会耗费太多的计算内存和时间,且在截断边界上应用第一类边界条件不会带来太大的截断误差。采用C++语言编程,提高了程序的执行效率。均匀全空间模型数值解与解析解的误差小于11%。利用全空间瞬变电场的解析式研究了全空间瞬变电、磁分量的扩散时空特征,计算结果表明全空间瞬变电磁场的扩散明显不同于半空间瞬变电磁场,电场分量类似水波一样向外扩散。数值计算结果表明高阻煤层对瞬变电磁场的扩散影响很小,而低阻煤层对瞬变电磁场的畸变作用很大,不利于开展瞬变电磁法。异常体的大小、空间形态、埋深、电阻率直接影响同点接收装置中的响应值。异常体的几何尺寸的变化对单个测点的响应值的影响是非线性的,增加到一定规模后影响逐渐变小。低阻异常体的埋深对同点装置响应值的影响较大,浅层低阻异常体中由一次场关断瞬间直接感应出的涡流电场非常强,远大于随后大地介质中扩散场在异常体中激发的涡流响应。异常体的空间形态的变化在测线上可以反映出来,倾斜异常体的响应特征与半空间存在一定的区别,反倾斜一侧的感应电动势大于另一侧。两种瞬变电磁掌子面超前探测方式均能反映前方低阻异常,短勘探线方式根据等值线的倾斜方向可以定性异常的方位,扇形观测对异常的定位更准确,理论上扇形观测方式效果更好。研究表明矿井瞬变电磁透视法可以有效地反映低阻异常的位置,新的探测方式有助解决当前施工模式下空间异常定位难、时深转换不准的困局。曲线对比法、异常体响应系数反投影成像法、几何成像法三种方法都能在一定程度上解释异常体的位置,其中异常系数反投影法效果最好,三种方法相结合可以提高解释的精度。矿井瞬变电磁透视法资料反演解释方面还有待进一步研究。
[Abstract]:The mine transient electromagnetic method is one of the most important methods for the construction of the prediction and prediction of the dangerous source of water inrush in the coal mine. It is one of the most important means of investigation in the comprehensive early warning model of the well and bottom. This method has the advantages of high efficiency and sensitive to the good guide water cut structure. The problems to be solved, such as small calculation apparent resistivity, space positioning and directional detection of geoelectric anomaly body, effective detection depth and time depth conversion, are discussed in this paper. In this paper, the numerical simulation method is used to study the response characteristics of the spatial anomaly body of the whole space. On the basis of previous studies, the paper derives the unconditionally stable Du Fort-Frankel difference scheme of the finite volume method (generalized difference method) based on the orthogonal hexahedral division based on the three-dimensional electric field diffusion equation, and avoids the need to calculate the derivative of the conductivity in the difference scheme constructed from the magnetic field diffusion equation. The analytical solution of the electric field of the uniform full space magnetic field is taken as the source of the initial condition. Under the large area condition, the non uniform grid space discrete method will not cost too much memory and time, and the application of the first kind of boundary conditions on the truncated boundary will not bring too much truncation error. The program is programmed with C++ to improve the range. The error of the numerical solution and the analytical solution of the uniform full space model is less than 11%.. The spatial and temporal characteristics of the whole space transient electric field and the magnetic component are studied by the analytical formula of the full space transient electric field. The calculation results show that the diffusion of the whole space transient electromagnetic field is obviously different from the half space transient electromagnetic field, and the electric field component is similar to the water wave. The numerical results show that high resistivity coal seam has little influence on the diffusion of transient electromagnetic field, while low resistivity coal seam has great effect on transient electromagnetic field distortion, which is not conducive to the development of transient electromagnetic method. The size of abnormal body, space form, buried depth, and resistivity directly affect the response value of the same point receiving device. The influence of the response of a single point on the response value of a single point is nonlinear, and the influence gradually becomes smaller after increasing to a certain scale. The depth of the low resistivity abnormal body has a great influence on the response value of the same point device. The direct induction of the eddy current field in the shallow low resistivity abnormal body is very strong, far larger than the anomalous diffusion field in the subsequent earth medium. The variation of the spatial form of the abnormal body can be reflected on the measuring line. The response characteristics of the abnormal body are different from the half space, and the induction electromotive force on the side of the reverse side is larger than the other side. The two transient electromagnetic palm front detection methods can reflect the front low resistivity anomaly and the short exploration line mode. According to the inclination direction of the contour line, the azimuth of the anomaly can be qualitative, the sector observation is more accurate for the location of the anomaly, and the effect of the fan-shaped observation is better in theory. The research shows that the mine transient electromagnetic perspective method can effectively reflect the position of the low resistivity anomaly, and the new detection method helps to solve the difficulty of the spatial anomaly location under the current construction mode and the time depth. Three methods, curve contrast, abnormal body response coefficient back projection imaging, and geometric imaging method can all explain the position of abnormal body to a certain extent, and the effect of abnormal coefficient back projection method is the best. The combination of the three methods can improve the accuracy of interpretation. Further research is still to be done.

【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P641.461;P631.325

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