Effects Of Formation Stress On Logging Measurements

Abstract

We show both theoretically and experimentally how stress concentrations affect the velocity field around a borehole surrounded by a formation with intrinsic ortohombic anisotropy. When F[subscript x] = F[subscript y], no extra anisotropy is induced, however, isotropic stress concentrations are developed in the neighborhood of the borehole. Extra anisotropy is induced only when F[subscript x] ≠ F[subscript y], and the level of induced anisotropy is affected by the intrinsic anisotropy of the formation. Experiments show that monopole acoustic waves are more sensitive to properties in the neighborbood of the borehole than dipole waves. However, only dipole logging can determine the direction of anisotropy. A combination of monopole and dipole logging may lead to a better investigation of intrinsic as well as induced anisotropy of the formation.