Abstract

A new logging-while-drilling (LWD) logging tool has been developed to measure shear wave anisotropy and provide a wellbore acoustic image. The tool consists of a focused transmitter and six focused receivers. The transmitter fires rapidly and waveforms are acquired in the six receivers as the tool rotates in the borehole. Sixteen azimuthal waveforms are acquired for each receiver and processed to produce compressional and shear velocities of the formation as a function of azimuth.

Anisotropy ratio and maximum/minimum stress directions are determined from the velocity images. Borehole images of the compressional and shear velocities of the formation are also obtained from the azimuthal velocities. This paper shows modeling data of the tool response in different anisotropic formations to assess the accuracy and viability of the measurement. The ability of the measurement to determine formation anisotropy at different borehole inclinations and the sensitivity of the borehole image to the formation acoustic properties are also discussed. Field examples of the anisotropy measurement and the borehole images obtained in vertical, deviated, and horizontal wells are presented.

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