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A borehole breakout forms when the concentrated compressive stress around a drilled hole fractures and removes part of its wall. Opposed damaged sectors widen the originally circular hole. A borehole televiewer images the wall so that the enlargement and its orientation can be distinguished from an isolated natural fracture.

For an approximately vertical hole aligned with a principal stress direction, the long axis of the breakout follows the minimum horizontal compressive stress direction. The strongest tangential compression occurs there even though the distant horizontal compression in that direction is smaller. Inclined holes, pore pressure, drilling pressure and rock strength require a fuller model before orientations or magnitudes are inferred.^[ref]

A borehole televiewer produces an oriented image of a borehole wall, often by scanning with acoustic pulses. Recorded echo amplitude and travel time reveal changes in wall reflectivity and radius as a function of depth and azimuth.

An enlarged cross-section can indicate borehole breakout, while fractures produce other characteristic traces. Inferring the surrounding stress requires a mechanical interpretation of those features; the image alone does not directly measure every stress component. Borehole conditions and tool orientation affect the result.