过套管电阻率测井大功率超低频信号源设计研究

Design of High Power and Ultra-low Frequency Signal Source in Cased Hole Resitivity Logging

过套管电阻率测井仪器的信号源位于地面,要求信号源具有大电压、大电流、超低频、高稳定度、高分辨率等特点。针对该测井技术的特点,提出利用直接数字频率合成技术产生要求的正弦测井激励信号,利用小功率低压器件的串联实现信号的大功率大电压输出,利用电源跟踪技术在一定程度上降低功率器件的损耗,提高电路的工作效率。实验结果表明,信号源输出频率1~15 Hz,频率分辨率为0.004 Hz,频率稳定度为±5×10-6/1 h,输出电压范围为±300 V,输出电流≤6 A,输出功率为900 W。该设计已成功用于过套管电阻率nV级极微弱电信号采集理论与实验研究项目中。

The cased hole resitivity logging technology is one of high-tech logging technologies being studied in China.The signal source of the logging instrument is located on the ground,which requires signal sources with high voltage,high current,ultra-low frequency,high stability,high resolution,etc.Based on the characteristics,proposed are the ideas that the direct digital synthesis technique should be applied to produce the required sine logging exciting signals,series devices of low power and low voltage are also used to produce the signals with high power and high voltage,and power tracking technique is used to some degree to lower the dissipation of power devices,and to improve the circuit working efficiency.The result of the experiment shows that the output frequency of signal source is 1~15 Hz,frequency resolution 0.004 Hz,frequency stability ±5×10-6 per hour,output voltage scale ±300 V,output current ≤6 A,output power 900 W.The design has been successfully applied in the research project of extremely weak nV-level electric signal acquisition theory and experimental study on formation resistivity measurement through metal casing.