Which term describes a borehole enlargement in a direction parallel to the minimum horizontal stress?

Which term describes a borehole enlargement in a direction parallel to the minimum horizontal stress?

• A. Borehole Breakout
• B. Stepout
• C. Microfracture
• D. Caving

Answer: (A)

Borehole breakout happens when rock around a drilled hole yields and opens up in a shear-driven way along the wall, creating enlargements that lie parallel to the minimum horizontal stress. The stress field around the borehole concentrates in such a way that the most favorable path for wall failure is along the direction of the least horizontal compressive stress, so the rock cracks and the borehole wall widens into an elongated shape oriented with that stress. This is the classic description of why the enlargement aligns with the minimum horizontal stress. Other terms don’t describe this directional enlargement: a microfracture is a small-scale crack, caving is a collapse into the hole under certain conditions, and a stepout refers to lateral distance or fracture propagation in another context, not the oriented enlargement of the borehole wall.

Borehole breakout happens when rock around a drilled hole yields and opens up in a shear-driven way along the wall, creating enlargements that lie parallel to the minimum horizontal stress. The stress field around the borehole concentrates in such a way that the most favorable path for wall failure is along the direction of the least horizontal compressive stress, so the rock cracks and the borehole wall widens into an elongated shape oriented with that stress. This is the classic description of why the enlargement aligns with the minimum horizontal stress.

Other terms don’t describe this directional enlargement: a microfracture is a small-scale crack, caving is a collapse into the hole under certain conditions, and a stepout refers to lateral distance or fracture propagation in another context, not the oriented enlargement of the borehole wall.