中心回线瞬变电磁全期视电阻率的计算研究

发布时间：2018-07-10 05:19

本文选题：瞬变电磁 + 中心回线　；参考：《西安科技大学》2017年硕士论文

【摘要】：瞬变电磁法(TEM)勘探装置类型众多,其中的中心回线装置效率高,优点突出,在工程找矿、煤矿水害预测等方面应用广泛。然而瞬变电磁施工时,在关断时间内一次场与二次场混叠,导致早期数据发生畸变,无法获取准确的浅部地层信息,给全期视电阻率的反演解释带来很大影响。为了获取地层在深度上视电阻率的连续变化特征,依据瞬变电磁中心回线装置均匀半空间电偶极子脉冲激发的垂直磁场理论,以线性斜阶跃电流关断起点为延迟采样零时刻的电偶源垂直磁场为例,根据单位脉冲响应函数的性质,本文将关断时间内线性斜阶跃的脉冲响应剖分为一系列垂直脉冲响应之和,建立起正演磁场响应和实测感应电动势转化的磁场响应之间的方程,再设置电阻率范围,采用优化的迭代算法计算出全期视电阻率,这样就可以解决关断时间对磁场的影响。通过对均匀半空间、两层模型、三层模型和四层模型不同参数下的地电模型进行数值模拟,验证了均匀半空间及多层介质模型的大地表面一维瞬变电磁正演程序的准确性,并总结出了各模型在参数变化时的磁场响应变化规律,对实际资料的解释有一定的参考价值。根据建立的全期视电阻率计算模型,本文编写了一维全期视电阻率计算程序,并对各地电模型的正演瞬变电磁响应进行反演,绘制全期视电阻率剖面图,再与正演计算出的全期视电阻率曲线和晚期公式计算的视电阻率曲线作对比。结果表明由本文模型计算出的全期视电阻率曲线能够与正演地电模型基本重合,而晚期视电阻率曲线在早期的视电阻率值偏大,不适合做全期解释。最后将研究成果应用于瞬变电磁实测资料的处理,并结合实际地质资料对结果进行验证。结果表明:全期视电阻率计算模型能够准确地反映出地层在深度方向的电阻率连续变化特征,且能够解决关断时间对磁场响应的影响,提高了瞬变电磁勘探的分辨率。
[Abstract]:Transient electromagnetic method (TEM) is widely used in engineering prospecting, coal mine water hazard prediction and so on because of its high efficiency and outstanding advantages. However, in transient electromagnetic construction, the mixing of primary field and secondary field in turn-off time leads to the distortion of early data and the inability to obtain accurate shallow formation information, which has a great influence on the inversion interpretation of the whole period apparent resistivity. In order to obtain the continuous variation characteristics of apparent resistivity in depth, the vertical magnetic field theory of uniform half-space electric dipole pulse excitation of transient electromagnetic center loop device is used. Taking the linear oblique step current turn-off starting point as the delay sampling zero time vertical magnetic field as an example, according to the property of the unit pulse response function, In this paper, the pulse response of linear oblique step in turn-off time is divided into the sum of a series of vertical pulse responses, the equation between the forward magnetic field response and the magnetic field response of the measured induction electromotive force transformation is established, and the resistivity range is set up. The effect of turn-off time on the magnetic field can be solved by using the optimized iterative algorithm to calculate the apparent resistivity of the whole period. Through the numerical simulation of the geoelectric model in homogeneous half-space, two-layer model, three-layer model and four-layer model with different parameters, the accuracy of the one-dimensional transient electromagnetic forward program on the earth surface of homogeneous half-space and multi-layer media model is verified. The variation law of the magnetic field response of each model is summarized, which has some reference value for the interpretation of the actual data. According to the whole period apparent resistivity calculation model, the one-dimensional full-period apparent resistivity calculation program is compiled in this paper, and the forward transient electromagnetic response of the local electric model is inversed, and the whole period apparent resistivity profile is drawn. The results are compared with the full-period apparent resistivity curve calculated by the forward modeling and the apparent resistivity curve calculated by the late formula. The results show that the full term apparent resistivity curve calculated by this model can basically coincide with the forward geoelectric model, but the late apparent resistivity curve is too large in the early stage to be interpreted throughout the whole period. Finally, the research results are applied to the processing of transient electromagnetic measured data, and the results are verified with the actual geological data. The results show that the whole period apparent resistivity calculation model can accurately reflect the continuous variation characteristics of resistivity in depth direction, and can solve the effect of turn-off time on magnetic field response, and improve the resolution of transient electromagnetic exploration.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.3

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