What term describes enlargements and elongations of a borehole formed by spalling parallel to the minimum horizontal stress?

• A. Drilling mud
• B. Borehole Breakout
• C. Erosion
• D. Casing collapse

Answer: (B)

Breakouts occur when rock around a drilled borehole fails and enlarges the hole in the plane aligned with the minimum horizontal stress. The near-wall rock experiences spalling along that least-stress direction, so the borehole wall bulges outward and becomes elongated parallel to the minimum horizontal stress. This is a telltale pattern used to infer the orientation of in-situ stresses. Other options describe different processes—drilling mud relates to fluid support rather than a failure shape, erosion is material removal by flow, and casing collapse is about the piping failing rather than widening the borehole wall.