The Effects of Stress Concentrations of Cased Hole on Induced Azimuthal Velocity Anisotropy

Abstract

In accordance with the need of estimating anisotropy and abnormal stress of formation by applying cross‐dipole logging to a cased hole, we show how stress concentrations affect the velocity distribution of formation around a cased hole, and how the velocity distribution influences the cross‐dipole anisotropy measurements by computing the stress distribution of a cased hole subjected to the tectonic stress and applying acoustoelasticity theory. The introduction of casing and cement in a cased hole results in a reduced range of stress concentration. The crossover of shear‐waves of radial polarization moves towards the borehole. The azimuthal extremum of shear‐waves is changed. But the azimuth of compressional velocity minima can still provide an excellent indicator of the direction of maximum far‐field tectonic stress.

Acoustoelastic effects of Stoneley waves in a borehole surrounded by a transversely isotropic elastic solid

“…6,[9][10][11][12][13][14]21 Most attempts from sonic logging assumed that the background formation is isotropic in the absence of stress. 6,[9][10][11][12][13][14]22 However, some rocks can exhibit anisotropy even in the absence of stress. 23 In petroleum seismology, we often encounter one of two types of anisotropy: transverse isotropy.…”