【作者】 孙天财；

【导师】 谢品芳；

【作者基本信息】 重庆大学 ， 电气工程， 2008， 硕士

【摘要】 瞬变电磁法是一种先进的地球物理勘探方法,已成功地应用于多个领域的深部测量,但这一技术由于发射、接收及数据处理各部分存在的问题使其在浅部测量中没有得到成功的应用。国内外学者经过多年研究,认为提高瞬变电磁法浅层分辨能力需要解决三个问题:减小发射电流关断时间;缩短测量回路的过渡过程;减小发射电流波形对测量结果的影响。本论文主要针对发射电流斜阶跃关断的斜阶跃场源,分析在斜阶跃场源激发下不同地电模型在三种常用测量装置下的瞬变响应,并根据这些瞬变响应进一步分析发射电流波形对测量结果的影响以及浅层测量对发射系统的要求,研究无需关断效应校正的直接计算全程视电阻率的数值计算方法。论文主要做了以下工作:①从瞬变电磁法原理出发,介绍了这种地球物理勘探方法的应用范围、常用测量装置及其异常特点、方法的优点以及目前还存在的问题。介绍并分析了目前就发射电流波形对测量结果的影响及校正方法的研究现状、“视电阻率”计算方法的研究现状,指出了它们的适用范围和需要改进之处。②介绍了不同地电模型在三种测量装置下负阶跃响应的由来,根据这些响应推导了各种模型在斜阶跃场源激励下感应段和衰减段的负斜阶跃响应,并从负阶跃响应与负斜阶跃响应的关系和磁场与磁场变化率的关系两方面证明了推导的正确性。分析了发射电流波形平稳性、对称性对二次感应电压的影响;以中心回线装置为例,分析了发射电流波形后沿对二次感应电压的影响,结合发射电流前沿与周期讨论了二者对感应段和衰减段二次感应电压的影响。③根据三种测量装置的负斜阶跃磁场和磁场变化率的解析表达式,分别讨论了感应段和衰减段的负斜阶跃磁场、感应电压与视电阻率的关系,给出了全程视电阻率的直接计算方法。最后用理论模型和实例计算证明了全程视电阻率直接算法的有效性。更多还原

【Abstract】 Transient Electromagnetic Method is a kind of advanced geophysics prospect methods, and is successfully applied to various fields of the deep soundings. However, this technology fails in resolving the shallow target in the vertical direction because of imperfectness of the transmitter, receiver and data-processing. After many years of research, scholars at home and abroad point out that enhancing the ability of shallow identification of this method needs to solve three key issues: reducing the turn-off time of the transmmitter current; shortening the the transition process of the receiver loop; eliminating the effect of transmmitter current wave on the sounding results.Transient response generated by ramp turn-off current is mainly studied in this paper. The transient response of several models under three commonly used measuring devices is analyzed. Based on these responses, the effect of transmitter current wave on sounding and the requirements of transmitter system for shallow measurement is further analyed. A numerical direct method of calculating the apparent resistivity without turn-off effect correction is studied. The main tasks of the thesis are presented as follows:Beginning with the principle of Transient Electromagnetic Method, the application fields, commonly used measurements devices, typical characteristics, as well as the existing problem of this method is introduced. The research status of the effect of transmitter current wave on sounding, turn-off effect correction as well as apparent resistivity calculation methods are introduced and analyed. The scope of these methods and need for improvement is also pointed out.The origin of responses generated by step turn-off transmitter current of several models with three commonly used measurements devices is introduced. Based on these responses, the responses generated by ramp turn-off transmitter current in induction stage and decay stage are derived. From two aspects—the limit and the special relationship between magnetic fields and time derivative of magnetic field,the correctness of the derivation is proved. The effect of stableness and symmetry of transmitter current wave on the second induction voltage is analyed. Taking central loop as an example, the effect of turn-off time on the induction voltage is analyed. The effect of forefront and cycle time of transmmitter current on induction voltage in induction stage and decay stage is discussed. According to the magnetic field and time derivative of magnetic field of three commonly used measuring devices, the relationship among magnetic field, induced voltage and apparent resistivity is discussed. A calculation method for all-time apparent resistivity is proposed. Finally, the practicability of the all-time apparent resistivity direct calculation algorithm is proved with theoretical models and field data experiments.更多还原