Characterization of overburden anisotropy improves wellbore stability in North Sea field

摘要

Borehole sonic data are traditionally used for both geophysical calibration and geomechanical modeling. However, in a strongly layered medium, compressional and shear sonic waves propagate at different speeds, depending on the orientation of the wellbore relative to bedding. This phenomenon, known as elastic anisotropy, is especially common in shale formations, where constituent plate-shaped clay particles are often oriented parallel to one another. When shales exhibit a vertical axis of symmetry roughly orthogonal to layering, they can be described by a form of elastic anisotropy known as transverse isotropy (TI), Fig. 1.