【作者】 刘志新；

【导师】 岳建华；

【作者基本信息】 中国矿业大学 ， 地球探测与信息技术， 2008， 博士

【摘要】 近几年,矿井瞬变电磁法在全国各个矿区逐渐得到了推广和应用,其应用效果和带来的经济和社会效益逐渐得到认可。但在矿井地质条件下,即巷道空间影响下瞬变电磁场在全空间内的分布规律没有得到系统的研究,研究巷道空间及空间内的金属体(工字钢、铁轨和金属锚网)对探测结果的影响规律是矿井瞬变电磁法资料解释及处理中的关键技术。本论文以均匀介质中瞬变电磁场响应理论为基础,编制了全空间瞬变电磁场正演模拟程序,结合数值计算和物理模型实验,总结了矿井地质条件下瞬变电磁场的分布规律。主要研究成果如下:1)研究了全空间条件下瞬变电磁场的传播规律。在早期阶段,感应电流集中分布于发射天线附近,电磁场主要反映地层浅部地质信息;在晚期阶段,高频成份被导电介质吸收,低频成份占主导地位,这时瞬变电磁场的传播主要是扩散过程,反映中深部的地质信息;2)研究了矿井瞬变电磁法最小及最大探测深度及其影响因素。由于采用多匝小回线天线,接收信号不仅包括探测目标体感应的有用地质信息同时还包括由于线圈产生的自感信号。在采样早期阶段线圈自感信号比目标体感应信号强,但其衰减速度较快。在线圈自感信号衰减时间范围内线圈自感信号与浅层地层介质感应信号很难分离,所以总存在一个无法分辨目标体感应信号的时间范围,这个范围则是矿井瞬变电磁法对应的探测盲区,即最小探测深度。线圈自感信号迅速衰减后,接收的信号主要为不同深度介质的感应信号。由于瞬变电磁场在介质中传播时能量不断地衰减,当能量衰减到一定程度时就不可分辨,无法识别更深地层介质的感应信息,所以对应一个最大探测深度;3)建立了全空间瞬变电磁场数学模型,并编写了三维有限元正演模拟程序。利用所编制的程序对不同模型及不同参数进行计算对比分析。在均匀全空间条件下分离回线装置与重叠回线装置所接收的感应信号衰减规律基本一致,但分离回线装置接收的响应值比重叠回线装置接收的响应值小,说明在相同条件下重叠回线装置的灵敏度较高;巷道空间的存在使瞬变电场响应值减小,但没有改变其整体上的衰减趋势。当巷道空间围岩介质中存在低阻异常体时,巷道空间对异常体响应曲线的影响主要集中在采样时间序列的早期阶段,而对采样时间序列的晚期阶段无影响,说明巷道空间的存在对浅层异常体的探测结果有影响,而且巷道空间越大,对探测结果影响越大;4)对巷道空间内金属体对感应场的干扰特征进行了物理模型实验:当天线位于巷道靠近探测目标体所在一侧时,接收到的响应值最高;当天线位于远离探测目标体一侧时,由于巷道空间的影响使探测结果的分辨能力降低。巷道内的金属体(工字钢、金属锚网和铁轨)使所接收到的信号值变大;5)根据数值模拟和物理模型实验结果,设计了矿井瞬变电磁探测方法与技术。如果探测目标体位于巷道顶板以上,同时巷道内有锚网支护底板上有铁轨时,发射接收天线置于巷道顶板;如果探测目标体位于工作面煤层,应将天线装置垂直巷道底板,并且靠近探测目标体所在巷道一侧,以获得探测目标体最大的感应信号;如果不能确定异常体的具体空间位置,应采用全方位探测技术。论文有图77幅,表4个,参考文献127篇。更多还原

【Abstract】 Mine transient electromagnetic method has been gradually popularized and applied in many mining areas in recent years. The applied effect, economic performance and social benefits have been acknowledged, but the basic theory, construction technology, data processing and display technique of mine transient electromagnetic method, all that adopt the research production of transient electromagnetic method on the ground. In mining geological conditions, it is said that under the influence of the roadway space, the regularities of distribution of transient electromagnetic field in the full space has not been complete researched at the present time. It is very important that research the influence law of roadway space and metal bodies (double T-iron, rail and metal netting) to the detecting data for transient electromagnetic method data processing and data explanation. The paper made a procedure to simulate the full space transient electromagnetic field, which based on the theory of transient electromagnetic field in homogeneous medium. The main research findings as follow:1) The propagation characteristics of full-space induction field of transient electromagnetic method were researched. The results indicated that the induced current mainly distributed on the surface of the geologic body and the response of transient electromagnetic field mainly reflects the superficial information of the stratums during the early stage. But during the late stage, the high frequency component was absorbed by electrical medium, so low frequency sign was dominant. The mode of transmission of transient electromagnetic fields was mainly diffuse process which reflects the information of the deep stratums.2) The minimal and maximum detecting depth and its influence factors were researched. The results indicated that the acquisition data included not only the useful geologic signal about the aim body, but also the self-induced signal that because of the multi-turn little coils. During early stage, the self-induction signal is stronger than the useful geologic signal. It is difficult to separate the self-induction signal and the shallow stratum signal. Therefore, there is a time range, during which we cannot separate the useful signal, so before this time is the detecting blind zone for transient electromagnetic method, which is the minimal detecting depth. After the attenuation of self-induced signal, the signal is mainly induced signal for vary depths. Because of the energy attenuation, when we cannot distinguish the induced signal of deeper-stratum, which is the maximum detecting depth.3) The mathematical model of the full-space transient electromagnetic fields was established and the finite element numerical simulation method of three dimensions transient electromagnetic field was studied. The concept of area coordinates and cubage coordinates were introduced during the liner interpolation process, which made the design procedure of the mathematical model becomes easier. The memorize technology of ultra-large sparse matrix was studied, which saves the memory and the computation time. Contrasted and analysed the response characteristic of transient electromagnetic field for different models and different parameters. The results indicated that the induced signal of separate loops and overlap loops has the same attenuation laws in the homogeneous whole space, but the field value of former is smaller than the field value of later, which shows that overlap loops has a better sensitivity in the same conditions. The roadway space minished the response value of transient electromagnetic field, but did not change the attenuation trend. When there is a low resistivity body in the medium around the roadway space, the effects of the roadway space shows only in early period. This shows that the superficial layer is affected by the roadway space, and the roadway space is bigger, the effects is stronger.4) Through the physical model experiment, the paper concluded that, when transmission and reception are placed beside the aim body, the response is the strongest, and when transmission and reception are placed faraway from the aim body, the sensitivity will fall greatly. The response values become strong for the metal body (double T-iron, rail and metal netting) in roadway space, but the features keep the same for the abnormal body. The accepted induced signals mainly come from the response of terra medium near the roadway side during the survey, which is that the distance between antenna and aim body is smaller, the response is stronger.5) Base on the result of numerical simulation and physical model experiment, we designed the construction technology of mine transient electromagnetic method: If the detecting target locates in roof, and there are railway rail on the floor, the antenna should been placed near the roof. But for the target that locates under the floor, the antenna should been placed on the floor. When we cannot confirm the specific spatial location, the omni-bearing detecting technology should been applied.更多还原