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

It is usually difficult to measure acoustic velocities through a 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 and to reduce the casing wave in the data acquisition process.In what follows,a theoretical modeling is used to caculate the wavefroms of cased wells.And then,a scaled experiment was conducted in the 1:10 scaled experimental well using the proposed technique in the poorlybonded condition.The results show that this technique can effectively suppress the casing wave and enhance the formation wave,even in the poorly-bonded condition.By analyzing the measured wavefroms,the amplitude of casing wave is reduced to 12%compared to the conventional one-source technique,and the compressional wave velocity can be easily obtained by using this technique.Both the theoretical modeling and experiment results demonstrate the feasibility of the proposed technique.This study establishes the theoretical and experimental foundation for the cased-hole,dual source of opposite polarity,acoustic logging tool development.