Sonic Logging in Deviated Boreholes of an Anisotropic Formation: Laboratory Study

Deepwater field development requires drilling of deviated or horizontal wells. Most formations encountered can be highly anisotropic and Pand S-wave velocities vary with propagation directions. Sonic logs acquired in these wells need to be corrected before they can be applied in formation evaluation and seismic applications. In this study, we make use of a laboratory model made of an approximate transversely isotropic Phenolite to study acoustic logging in deviated wells. We drill holes at various deviations relative to the symmetry axis in the Phenolite block. Then we perform monopole and dipole sonic measurements in these holes and extract the qP, qSV, SH, and Stoneley wave velocities using the slowness-time domain semblance method. The velocities measured using monopole and dipole loggings vary with borehole deviations. We also measure the qP, qSV, and SH wave velocities using body waves at the same angles as the well deviations. We then compute the theoretical qP, qSV, SH, and Stoneley wave velocities based on an equivalent transverse isotropic model of the Phenolite. We find the qP, qSV , and SH wave velocities obtained using the body wave measurement and acoustic logging method agree with the theoretical predictions. The Stoneley wave velocities predicted by the theory also agree reasonably well with the logging measurements.