Radial detection depths of borehole Stoneley modes

Abstract

Propagation features of Stoneley modes are widely used for measurements of reservoir permeability and rock anisotropy in acoustic logging. Through the finite difference algorithm, the radial detection depth of the Stoneley wave along a fluid-filled borehole is investigated. The radial variations of the displacement components Ur for Stoneley wavefronts are presented as the particle motions in that direction are controlled by the permeability and transverse shear modulus of the medium surrounding the wellbore. It is shown that the Stoneley-wave energy reaches a peak value at the borehole wall and attenuates exponentially with the increasing radial depth in the formation. By comparison of reflected Stoneley-wave amplitudes from reflectors with various distances to the borehole wall, the prospecting depths of Stoneley modes can be confirmed. It is generally no more than 0.2 meters with the frequency range of acoustic logging. This result reveals that only a very shallow region around the wellbore can be detected from the Stoneley-wave responses.