过金属套管电磁响应的频率特征研究

Study on Frequency Characteristics of Through Casing Electromagnetic Responses

在有金属套管的井中通过测量电磁响应的方法获取套管外地层电阻率时,电磁信号的频率至关重要。采用解析法正演计算了在不同频率的源信号激励下金属套管外的电磁响应,分析得出发射源频率约在126Hz时可以获得最佳观测信号。为了验证计算的结果,利用实验室模拟装置进行了实验室物理模拟,结果验证了计算结果的正确性。研究结果也表明,采用最佳频率激励的电磁场能穿透金属套管并产生随地层电阻率变化的电磁响应。

Source frequency was a key factor for obtaining optimum observation of electromagnetic responses in-situ or on surface to deductive formation resistivities.The optimum frequency for electromagnetic field to penetrating the simulated metal casing was about 126Hz by analyzing the electromagnetic responses calculated by analytic solution of controlled source responses of cased well model.A laboratory analogue model was set to carry out the measurements of electromagnetic responses through casing.For the purpose of proving calculation result,laboratory physical simulation was conducted by using simulation apparatus and the calculating correctness was proven by simulation result.The results show that electromagnetic field can penetrate the metal casing and the responses observed can well reflect the variation of the formation resistivity outside of casing if the exciting field is in optimum frequency.