大回线瞬变电磁法浅层探测研究

发布时间：2018-02-28 02:49

本文关键词： 瞬变电磁法浅层勘探盲区大回线源正演　出处：《煤炭科学研究总院》2017年硕士论文　论文类型：学位论文

【摘要】：瞬变电磁法是地球物理勘探领域中一种重要的探测方法,应用十分广泛。但在实际工作中,对瞬变电磁法用较大发射线框探测近地表目标体的应用较少。针对这样的情况,本文着重研究大回线源瞬变电磁法对浅层异常体的探测效果。在发射电流为斜阶跃波形的基础上,对探测浅层目标体的几个问题进行了重点探讨,希望给实际工作提供一定的参考和依据。论文对大回线源一次场的分布规律进行了分析,得出磁场强度随深度的增加而减小。这说明相对于深部地层,浅部地层被激发的程度大,是一次场形成的优势区域。在此基础上,还总结了不同发射线圈的一次场能量分布特征,推导了深度和最大激发边长的关系式。分析了解释盲区和理论勘探盲区的区别。建立了含有浅层异常体的地质模型,进行正演计算,研究浅层探测效果。为了符合实际情况,得到纯二次场的观测数据,对一次感应电压在接收线圈中的过渡过程进行了研究,计算出了不同发射线圈的最小可分辨时间,在后续的资料处理中,舍弃了观测数据中早期受一次场干扰的数据,然后运用晚期公式计算了视电阻率。理论模拟结果说明较晚时间的观测数据包含浅层地质信息,瞬变电磁法不存在理论勘探盲区。其中,异常体的埋深分别为Om、10m、20m时,所得处理结果都对异常体有明显反映。其次,对同一个浅层异常体,用不同边长的发射线圈进行观测,所得处理结果都可以反映异常体的存在;在同一观测系统下,讨论了不同电阻率的异常体的处理结果,同时也讨论了不同电阻率的覆盖层下异常体的处理结果,对异常体都有良好的反映。最后,结合试验,在一个浅层含有积水采空区的区域进行实际观测,目标层埋深为地下20m～50m左右。在试验结束之后,经钻孔验证,推断(积水)采空区与钻探结果基本吻合,说明本次探测成果比较可靠,同时也说明大回线源探测浅层异常体可以取得较好的效果。
[Abstract]:Transient electromagnetic method (TEM) is an important detection method in the field of geophysical exploration and is widely used. However, in practical work, there are few applications in detecting near-surface objects by using large emission-line frames. This paper focuses on the detection effect of large loop source transient electromagnetic method on shallow anomalous bodies. On the basis of the oblique step waveform of emission current, several problems of detecting shallow objects are discussed emphatically. It is hoped to provide some reference and basis for practical work. In this paper, the distribution law of primary field of large loop source is analyzed, and it is concluded that the intensity of magnetic field decreases with the increase of depth, which indicates that the intensity of magnetic field decreases with the increase of depth. The shallow strata are the dominant region for the formation of the primary field, and the characteristics of the primary field energy distribution of the different emission coils are also summarized. The relationship between depth and maximum excited side length is derived. The difference between the interpretation blind area and the theoretical exploration blind area is analyzed. The geological model containing shallow anomaly body is established, the forward modeling is carried out, and the shallow layer detection effect is studied. The observation data of pure secondary field are obtained. The transition process of primary induction voltage in receiving coil is studied, and the minimum resolution time of different transmitting coil is calculated. In the subsequent data processing, The apparent resistivity is calculated by using the late formula. The results of the theoretical simulation show that the observation data of the later time contain shallow geological information. There is no theoretical exploration blind area in transient electromagnetic method. When the buried depth of anomalous body is 10 m or 20m, the results obtained reflect the abnormal body obviously. Secondly, the same shallow anomalous body is observed with different side length emission coils. Under the same observation system, the processing results of different resistivity anomaly bodies are discussed, and the processing results of abnormal bodies under different resistivity layers are also discussed. The results show that the depth of the target layer is about 20 m ~ (50 m) underground. After the experiment is finished, it is verified by borehole that the depth of the target layer is about 20 m ~ (50 m). It is inferred that the goaf is consistent with the drilling results, which shows that the detection results are reliable, and it also shows that the large loop source can obtain good results in detecting shallow anomalous bodies.
【学位授予单位】：煤炭科学研究总院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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