瞬变电磁法圆锥型场源响应特征理论研究

发布时间：2018-02-06 02:18

本文关键词： 瞬变电磁圆锥型场源互感系数关断时间暂态过程 “烟圈”反演拟MT反演　出处：《东华理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：传统地面大尺寸瞬变电磁激发源常用于以深部探测为目的的水文地质勘查和金属矿勘探等领域。随着瞬变电磁法的应用范围不断扩展至煤矿巷道、工程隧道等地下有限空间以及城市和工程浅层探测,常规大尺寸激发源受到限制,小型装置成为常用的工作装置。传统的瞬变电磁小型装置主要以共轴和偶极装置为主,为增强发射的初始电磁能量,通常采用多匝绕制的方法来增大发射磁矩,以此达到减少发射线圈边长与面积的目的。但是,这种发射和接收线圈的重合绕制方式造成了线圈内和线圈间的强互感耦合作用,进而使得关断效应影响增强,浅部“盲区”增大。为此,本文从场源角度出发,提出了一种圆锥型场源装置,对其响应特征开展了理论研究。推导了该装置内各匝线圈半径的计算公式,根据叠加原理的思想讨论了圆锥型场源瞬变电磁的正演方法,应用快速汉克尔变换,G-S变换及正、余弦变换数值滤波算法进行了数值计算。对圆锥型场源一次场、二次场特征进行了分析,计算并比较了不同参数下圆锥型场源和多匝线圈的互感系数和关断时间。研究发现:对于等效磁矩为926.1Am2的多匝回线和圆锥型场源,前者的互感约为后者的9倍,关断时间约为后者的8倍;增大圆锥型场源的高度可减小互感系数,但其底半径的进一步变化对互感影响有限;圆锥型场源一、二次场特征与多匝线圈相似,但其二次场和总场暂态响应强于多匝线圈。应用平移算法求取了圆锥型场源瞬变电磁的全区视电阻率,根据瞬变电磁场传播的“烟圈”效应,对圆锥型场源瞬变电磁数据进行了“烟圈”反演;采用对应的时间-频率转换关系进行了圆锥型场源瞬变电磁测深数据到MT平面波场数据的等效转换,以“烟圈”反演结果作为初始模型,应用最小二乘正则化反演技术对圆锥型场源全区视电阻率数据进行了拟MT优化反演;以电阻率为100?·m的均匀半空间模型对两种反演方法进行了验证,结果表明改进后的反演电阻率与模型电阻率的相对误差约为0.2%,而“烟圈”反演的相对误差超过0.8%,并在此基础上对二层、三层和四层典型地电模型开展了正反演计算;最后,在某矿集区开展了短剖面试验,并采用两种反演方法对实测数据进行了处理。研究结果表明:用最小二乘正则化方法改进后的反演电阻率更接近于模型电阻率,反演深度更接近层界面,具有一定的分层效果,其视电阻率拟合曲线与模型的重构误差在10-4~10-3范围内。本文的研究成果表明,圆锥型场源装置对于减弱线圈间的互感,提升小装置瞬变电磁法的浅部探测能力具有重要的理论意义和应用价值。为了继续丰富、完善本方法,今后的研究重点应集中于圆锥型场源响应的后延影响改正,滤波技术适用性以及多维正、反演成像等领域。
[Abstract]:Traditional large size transient electromagnetic excitation sources are often used in hydrogeological exploration and metal mine exploration for deep exploration. With the application of transient electromagnetic method to coal mine roadway. Limited underground space, such as engineering tunnels, as well as urban and engineering shallow exploration, the conventional large-scale excitation source is limited. The traditional transient electromagnetic devices are mainly coaxial and dipole devices. In order to enhance the initial electromagnetic energy of emission, the multi-turn winding method is usually used to increase the emission magnetic moment. In order to reduce the side length and area of the transmitting coil, however, the coiling of the transmitting and receiving coils leads to the strong mutual inductance coupling between the coils and the coils, which makes the effect of turn-off enhanced. In this paper, a conical field source device is proposed from the point of view of field source. The response characteristics of the device are studied theoretically, and the formulas for calculating the radius of each turn coil in the device are derived. According to the principle of superposition, the forward modeling method of conical field source transient electromagnetic is discussed, and the fast Hankel transform is applied to G-S transform and forward. The numerical filtering algorithm of cosine transform is calculated and the characteristics of the primary and secondary fields of conical field source are analyzed. The mutual inductance coefficient and turn-off time of conical field source and multi-turn coil under different parameters are calculated and compared. It is found that for multi-turn loop and conical field source with equivalent magnetic moment of 926.1 Am2. The mutual inductance of the former is about 9 times of that of the latter, and the closing time is about 8 times of the latter. Increasing the height of the cone field source can reduce the mutual inductance, but the further change of the base radius has limited influence on the mutual inductance. The characteristics of the first and secondary fields of conical field are similar to those of multi-turn coils, but the transient responses of secondary field and total field are stronger than that of multi-turn coils. The apparent resistivity of transient electromagnetic field of conical field source is obtained by using the translation algorithm. According to the "smoke ring" effect of transient electromagnetic field propagation, the "smoke ring" inversion of the conical field transient electromagnetic data is carried out. Using the corresponding time-frequency conversion relation, the equivalent conversion from the conical field source transient electromagnetic sounding data to the MT plane wave field data is carried out, and the "smoke ring" inversion result is taken as the initial model. Using the least square regularization inversion technique, the quasi-MT optimization inversion of the whole area apparent resistivity data of conical field source is carried out. With a resistivity of 100? The results show that the relative error between the improved inversion resistivity and the model resistivity is about 0.2%. The relative error of "smoke ring" inversion is more than 0.8, and on the basis of this, the forward and inverse calculations are carried out for typical electrical models of two, three and four layers. Finally, a short profile test was carried out in a mine concentration area. Two inversion methods are used to process the measured data. The results show that the inversion resistivity is closer to the model resistivity and the inversion depth is closer to the layer interface with the least square regularization method. The reconstruction error between the apparent resistivity fitting curve and the model is in the range of 10 ~ (-4) ~ (-3). The research results in this paper show that the conical field source device can weaken the mutual inductance between the coils. It is of great theoretical significance and practical value to enhance the shallow detection capability of the transient electromagnetic method for small devices. In order to continue to enrich, the method is improved. The future research should focus on the correction of the delayed effect of the conical field source response, the applicability of the filtering technique, and the multi-dimensional positive and inverse imaging.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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