| Well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross-sectional shape of the borehole from circular to roughly elliptical. In vertical holes drilled in areas where one principal stress (Sv) is vertical, breakouts tend to form at opposite ends of the borehole diameter parallel to the least compressive horizontal principal stress direction (Sh). This paper uses an analytical elastic solution for stress at the wall of a borehole to analyze the rotation of breakout orientations away from the direction of Sh as the borehole deviates from the direction of the vertical principal stress. -- Mastin, 1988 |
