| open hole [`ō·pǝn `hōl] ENGINEERING 1. A well or borehole, or a portion thereof, that has not been lined with steel tubing at the depth referred to. 2. An unobstructed borehole. 3. A borehole being drilled without cores. PETROLEUM ENGINEERING In an oil-drilling operation, the unprotected hole which lies below the shoes of the last landed string of casing. |