层状介质上双频激电的电磁耦合效应

ELECTROMAGNETIC COUPLING EFFECT IN DOUBLE-FREQUENCY IP SURVEYS OVER A MULTI-LAYER EARTH

从电偶极子谐变电磁场的基本公式出发,研究了层状介质上双频激电的电磁耦合特点。经研究表明,用中梯、偶极装置观测层状介质,电磁耦合随任意层电阻率值变大而减小;随低阻层的相对变薄而变小;随收发距的减小而减小。此外,用中梯测量时,电磁耦合在AB(供电极距)中部最强,远离中部时耦合效应会逐渐减小;且供电极距越小、离主测线越远,电磁耦合也越小。而用偶极测量时,供电极距的变化对电磁耦合的影响比中梯小。

According to the basic equations for the harmonic electromagnetic field of electric dipole,the authors have studied the electromagnetic coupling effect in double-frequency IP surveys over a multi-layer earth.Several examples illustrate the characteristics of it.With decreasing the resistivity of arbitrary layer,the thickness of the low resistivity layer and the distance between transmitter and receiver,electromagnetic coupling both in central gradient array and dipole-dipole array tend to reduce.Additionally,electromagnetic coupling in central gradient array in the middle of power-supply polar distance is greater than other positions,and leaving from it and from main survey line,this effect will be down.We also find when power-supply polar distance becomes small,electromagnetic coupling is going to be reduced.But it seems less obvious in the dipole-dipole array because of the setting itself.