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在CSEM野外工作中,通常把接收机置于离源3～5倍趋肤深度以外的远区。本文从正演和反演两个角度研究了当源和接收机之间存在导电体时,该导电体对远区中目标体响应的影响。2D有限元正演结果表明导电体主要影响中低频的观测结果,导电体的电导率越低,尺寸越大,影响也越大,并且影响程度随着观测频率的降低而逐渐加大。反演结果表明若不考虑源和勘探区间导电体的存在,反演得到的目标体横向位置会向源的方向移动,带来解释上的误差。在CSEM实际工作中,应该是采用多方位的场源作三维采集和三维反演,以减少源和勘探区间低阻体的影响。
In CSEM field work, the receiver is usually placed far away from the source 3 to 5 times the skin depth beyond the remote area. In this paper, we study the effect of the conductor on the target response in the far region when there is a conductor between the source and the receiver from both forward and inverse angles. 2D finite element forward results show that the conductor mainly affects the low and middle frequency observations. The lower the conductivity of the conductor, the larger the size and the larger the influence, and the more the influence increases with the decrease of the observation frequency. The inversion results show that if the existence of the conductor between the source and the exploration interval is not considered, the horizontal position of the target body will be moved towards the source, resulting in an explanation error. In the practical work of CSEM, multi-directional field sources should be used for 3D acquisition and 3D inversion to reduce the influence of low-resistivity sources in the source and exploration intervals.