A cased-hole acoustic logging technique using the dual source of opposite polarity

It is usually difficult to measure acoustic velocity through casing, especially when the casing is poorly bonded with formation. An acoustic logging technique using the dual source of opposite polarity is proposed to enhance the Signal to Noise Ratio of the formation signal while reducing casing wave in the data acquisition process. In what follows, theoretical modeling is used to caculate the wavefroms of cased wells. Then a scaled experiment was conducted in the 1:10 scaled experimental well using the technique in the poorly bonded condition. The results show that this technique can effectively suppress casing wave and enhance formation wave, even in the poorly bonded condition. By analyzing the measured wavefroms, the casing wave amplitude is reduced to 12% and the compressional wave velocity can be easily obtained from the measurement technique. Both the theoretical modeling and experiment results demonstrate the feasibility of the proposed technique. This study establishes the theoretical and experimental foundation for cased-hole dual source of opposite polarity acoustic logging tool development.