【作者】 董毅；

【导师】 解海军；

【作者基本信息】 西安科技大学 ， 地球探测与信息技术， 2017， 硕士

【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。更多还原

【Abstract】 The transient electromagnetic detection device has many types,that the central loop is used widely in engineering and mineral prospecting and water disaster predication in the coal mine,ect,because of its higher work efficiency and many outstanding advantages.However,during the transient electromagnetic exaction,the primary field and second field are aliasing in turn-off time,which causes early data distortion,and be unable to obtain accurate information in shallow stratum,and has much inflluence on inversion interpretation of all time apparent resistivity.In order to acquire the continuous variation characteristics of stratum apparent resistivity in depth,according to pendicular magnetic field stimulated by electric dipole pulse in homogeneous half-space field of in loop of transient electromagnetic method,taking the start turn-off time of the linear ramp waveform current as zero time of delay sampling about electric dipole vertical magnetic field.According to the nature of unit pulse response function,this paper divides pulse response of linear ramp waveform to the total of a series of vertical pulse response,and establishes equation about magnetic field between forward and converts from measured induced electromotive force,then sets the rang of resistivity,using optimized iterated algorithm,which can eliminate effect of turn-off time on magnetic field.Through geoelectric model of numerical simulation under various parameters for homogeneous half space,two-layer model,three-layer model and four-layer model,the paper has verified the accuracy of one-dimensional transient electromagnetic forward program on earth surface of homogeneous half space and multilayered model,and summaried magnetic field response laws on various models in different parameter,which can provide reference value for Interpretation of actual data.According to the established all time apparent resistivity calculation model,this paper compiles one-dimensional all time apparent resistivity calculation program,and taked transient electromagnetic response from forward of each geoelectric model to inverse,and draws full time apparent resistivity profile,then compares to all time apparent resistivity decay curve that from forward and late time apparent resistivity delay curve.The result shows that all time apparent resistivity decay curve calculated by model from this paper can basically be coincident with geoelectric model from forward,but the value of apparent resistivity in early stage is superior for late time apparent resistivity delay curve,which is not suitable for full term interpretation.Finally,using the research result to deal with transient electromagnetic data,and combining with the actual geological data to verificate results.The results show that all time apparent resistivity calculation model can reflect stratum continuous variation of resistivity exactly in depth,and solve the influence of turn-off time to magnetic response,which can also improve the accurecy of all time apparent resistivity interpretation of transient electromagnetic method.更多还原