| dril. |
Cored Bit (CR; The centermost cutters of this bit were damaged by a rock core that was left in the hole by the preceding bit. This is merely one way in which a bit can core. A bit often cores when the nose part of one or more cones is broken, or when the abrasiveness of the formation exceeds the wear resistance of the center cutters. Improperly breaking in a new bit after a major change in the bottom hole pattern also can result in coring. A bit will also core when cutters are lost because of cone shell erosion, or when junk left in the hole breaks the center cutters. Kenny Gray) |
