Abstract Sonic data are an important input to geomechanics models, and logging while drilling (LWD) sonic tools are an important source of these logs. A case study is presented from a field within the Llanos basin of Colombia where the field operator experienced wellbore stability problems in a 12 1/4‑in. hole section and needed to update the geomechanics model so the optimal mud-weight program and trajectories could be chosen. Collecting reliable LWD sonic logs, particularly formation shear-slowness logs, was challenging because both fast and slow formations were encountered within a single bit-run and, consequently, both high-frequency refracted shear and low-frequency quadrupole modes were required to obtain reliable formation shear-slowness values at all depths. This required the firing of multiple transmitter modes over a broad-range of frequencies and recording and storing the resulting large quantity of data for subsequent processing. How the required can be reliably recorded with the latest LWD sonic tools, and how the formation shear-slowness can be derived from the LWD quadrupole mode are described.