Abstract

We have found in field observations that the multipole sonic logging tool can effectively measure formation P-wave and S-wave data in a cased hole. The multipole tool, containing both monopole and quadrupole source-receiver systems, was originally designed to log P- and S-waves directly, in all lithologies, for an open borehole. The monopole source-receiver system (P-wave) operates at 7-10 kHz, as compared with 15-25 kHz for a conventional sonic tool, while the quadrupole source-receiver system (S-wave) operates at 3-7 kHz. These lower operating frequencies enable the signals to penetrate the well casing and cement more effectively than signals from a conventional sonic tool. As a result, the formation P- and S-waves recorded by the multipole tool are generally much stronger than the unwanted waves which travel along the well casing and cement. Formation arrivals can be easily identified and separated from the casing arrivals for a wide range of lithologies. Logs run before and after the wells were cased show remarkable agreement even in severely washed out zones.

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