电性源短偏移距瞬变电磁法全程视电阻率计算研究

发布时间：2018-06-23 15:08

本文选题：瞬变电磁法 + 全程视电阻率　；参考：《东华理工大学》2015年硕士论文

【摘要】：随着矿产开发力度的加大,浅部矿产资源,已大幅减少。开展第二深度空间(500m~2000 m)矿产资源的精细勘探已成为一项紧迫和长期的任务。我国找矿的主体也正在向深部矿、隐伏矿发展,地球物理勘探成为隐伏矿产资源调查越来越重要的手段,开展大深度、高精度地球物理探测研究是当前物探所面临的主要科学问题。近年来,瞬变电磁法在矿产勘探领域得到广泛应用。但回线源瞬变电磁法仅对低阻异常敏感,对高阻异常的探测能力较弱,且勘探深度有限。LOTEM虽然可以观测磁场垂直分量和电场水平分量,对低阻和高阻异常都有较好的反映,但因收发距离较大,信噪比降低,不利于高效、精细探测。根据瞬变电磁场基本理论,当选择适当的发射波形激发电磁场时,接地导线源可以实现近源观测。在此基础上提出的电性源短偏移距瞬变电磁法(SOTEM)是一种探测深度大、精度高、施工高效的瞬变电磁工作形式。视电阻率作为电磁法数据解释的主要甚至唯一参数,在SOTEM系统中具有举足轻重的作用。由于SOTEM观测全场区信号,因此精确的全程视电阻率计算方法对于充分展现SOTEM的探测能力是十分重要的。本文从麦克斯韦方程出发,借助辅助位函数,求取电性源在均匀大地表面及层状大地表面产生的响应。将长接地导线源响应分成线源项和接地项分别计算,大大节省了计算时间。其次,通过扩散场平面传播分布图、单点衰减曲线对电性源激发的二次电磁场各分量进行研究,为实际工作选取合适的观测分量和观测范围提供了理论支持。运用分段级数逼近法、二分法、平移算法分别对磁场垂直分量及其随时间的导数进行了全程视电阻率求取,并对三种全程视电阻率提取方法的优劣以及基于磁场强度和感应电动势计算的全程视电阻率的对薄层的分辨能力进行了分析。全程视电阻率曲线特征,与早、晚期视电阻率相比,对电性目标体反映更准确,能较准确地反映地电断面的信息。另外,全程视电阻率仅与地层的电性结构有关,与收发距、方位角无关,便于野外进行接地源瞬变电磁近源测量。最后将本文提出的全程视电阻率计算方法应用于某金属矿探测,取得了较好的地质成果。通过理论分析和实例应用,证明本文提出的电性源瞬变电磁全程视电阻率计算方法的有效性。全程视电阻率消除了浅部的假高值现象,明显优于传统晚期视电阻率,相对真实地反映出地层的电性变化规律。
[Abstract]:With the intensification of mineral exploitation, shallow mineral resources have been greatly reduced. It has become an urgent and long-term task to carry out fine exploration of mineral resources in the second depth space (500m~2000 m). The main body of prospecting in our country is also developing towards deep ore and hidden ore. Geophysical exploration has become an increasingly important means for the investigation of hidden mineral resources and has been carried out in a large depth. High-precision geophysical exploration is the main scientific problem in geophysical exploration at present. In recent years, transient electromagnetic method has been widely used in the field of mineral exploration. However, the transient electromagnetic method of loop source is only sensitive to low resistivity anomalies and weak in detecting high resistivity anomalies. Although the exploration depth is limited, the vertical and horizontal components of magnetic field can be observed, and both low resistivity and high resistivity anomalies can be well reflected. However, because of the large transceiver distance and the lower signal-to-noise ratio, it is unfavorable to high efficiency and fine detection. According to the basic theory of transient electromagnetic field, the near-source observation can be realized by grounding wire source when proper transmitting waveform is selected to excite the electromagnetic field. On this basis, the short offset transient electromagnetic method (SOTEM) for electrical source is proposed, which is a kind of transient electromagnetic working form with high detection depth, high precision and high construction efficiency. As the main or even the only parameter in the interpretation of electromagnetic data, apparent resistivity plays an important role in SOTEM system. Due to the whole field signal observed by SOTEM, it is very important to calculate the whole apparent resistivity of SOTEM accurately in order to fully demonstrate the detection ability of SOTEM. Based on Maxwell's equation and auxiliary potential function, the response of electrical source on homogeneous and stratified geodetic surface is obtained in this paper. The response of long grounding wire source is divided into line source term and grounding term, which greatly saves calculation time. Secondly, through the plane distribution of diffusion field and the single point attenuation curve, the components of the secondary electromagnetic field excited by the electric source are studied, which provides theoretical support for the practical work to select the appropriate observation component and observation range. Using the piecewise series approximation method, the dichotomy method and the translation algorithm, the whole apparent resistivity of the vertical component of the magnetic field and its derivative with time are obtained, respectively. The advantages and disadvantages of three methods for extracting the whole process apparent resistivity and the resolution ability of the whole process apparent resistivity based on magnetic field intensity and induction electromotive force are analyzed. Compared with the early and late apparent resistivity, the characteristics of the whole apparent resistivity curve are more accurate to reflect the electrical target body, and can accurately reflect the information of the geoelectric section. In addition, the whole apparent resistivity is only related to the electrical structure of the formation, independent of the transceiver distance and the azimuth, so it is convenient to measure the earthing source transient electromagnetic near source in the field. Finally, the whole apparent resistivity calculation method proposed in this paper has been applied to a certain metal ore exploration, and good geological results have been obtained. Through theoretical analysis and practical application, it is proved that the proposed method for calculating the whole apparent resistivity of transient electromagnetic source is effective. The whole apparent resistivity eliminates the false height phenomenon in the shallow area and is obviously superior to the traditional late apparent resistivity and reflects the electric change law of the formation.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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