A multipole sonic-while-drilling service combines high-quality monopole and quadrupole measurements to deliver robust compressional and shear slowness - along with enhanced Stoneley data - in a wide range of applications, regardless of mud slowness. Compressional and shear data from the service showed very good agreement with monopole compressional and shear data from a wireline acoustic scanning platform. This sonic information is valuable not only for drillers, but also for geophysicists, geologists, petrophysicists, and reservoir and completion engineers.
To achieve such measurement outcomes, the design of the tool is critical. However, designing a logging-while-drilling (LWD) sonic tool is difficult. The effects on the measurement from the complexity of the acoustic propagation coupled with the presence of the collar in the well make development of such a tool a challenge. In addition, the interference of the collar arrival with compressional head waves as well as the collar's impact on other modes such as Stoneley and quadrupole calls for a detailed and accurate design. Finally, because the LWD tool occupies a significant area of the borehole cross section, its presence impacts the character of dispersive modes.
A methodology based on modeling was used to design an effective LWD tool. The design was then tested in a field test and results were compared with wireline measurements.
