瞬变电磁测井原理研究Ⅳ:二维谱  

Theory Study for Transient Electromagnetic LoggingⅣ:2DSpectrum

作　　者：臧德福 朱留方 沈洪楚 沈永进[2] 沈建国[2] 

机构地区：[1]中石化胜利石油工程有限公司测井公司,山东东营257096 [2]天津大学电子信息工程学院功率超声实验室,天津300072

出　　处：《测井技术》2015年第1期15-20,共6页Well Logging Technology

摘　　要：在井条件下解Mexwell方程研究裸眼井的瞬变电磁测井低频响应及其二维谱,频率范围为1～30 Hz.低频段的响应主要受地层电导率影响;电磁波传播速度很低,传播过程不明显,满足电磁感应原理,其二维谱主要刻画电磁感应现象.二维谱的实部很大,虚部很小,对应的测井响应中与地层电导率参数无关的直接耦合信号幅度很大,反映地层电导率的响应幅度很小.将不同地层电阻率的响应波形相减得到的响应差与地层电阻率有关,电阻率越大,响应差的峰值越大;响应差的峰值偏离激发波形突变位置,接收线圈距离发射线圈越远,响应差的峰值偏离波形突变位置的时间越大.这些差别刻画了瞬变电磁测井的主要特征是由地层的电导率产生的.To get transient electromagnetic logging response, it is necessary to solve Maxwell equation under the condition of borehole, Its solution and two-dimensional spectrum describing the characteristics of logging responses can be obtained by analysis method. The low-frequency response and two-dimensional spectrum of transient electromagnetic logging of borehole in frequency range of 1~30 Hz are given. The low-frequency response describes the principle of electromagnetic induction and is mainly affected by stratum conductivity. It is not obvious to display the process of propagation of the electromagnetic wave. The real part of the two- dimensional spectrum is larger, yet the imaginary part is smaller. So the response amplitude is consisted by direct induction which is not affected by stratum conductivity. Subtracting the response waveforms of the different stratum conductivity, it is found that the larger the resistivity is, the larger the peak value of the response difference. The peak value of the response difference apart from the position of the excitation current, the closer receiving coil is to transmitting coil, the greater peak value of the response difference. These differences describe the main characteristics of transient electromagnetic logging.

关 键 词：瞬变电磁测井 二维谱 电磁波 电磁感应 电导率 差值 

分 类 号：P631.83[天文地球—地质矿产勘探]