Determination of Shear Wave Velocities in "Slow" Formations

Abstract

Direct determination of formation shear wave travel time is impossible in "slow" formations where the shear wave velocity is lower than the borehole fluid (mud) velocity. However, the Stoneley waves in these formations are very sensitive to changes in formation shear wave properties and can be used to indirectly determine the formation shear velocity, In addition, the P wave packet is highly dependent on the Poisson's ratio and thus can be used to estimate the shear velocity once the P wave velocity is known. These phenomena are demonstrated with both numerical and field examples.