Irregular tooth spacing reduces roller cone bit tracking problems
- Hughes Christensen Co., Houston, TX (United States)
- Transatlantic Technical Services, Houston, TX (United States)
On tungsten carbide insert bits, irregularly spaced teeth can help stop tracking problems, leading to increased penetration rates and longer bit runs. Tracking, which occurs when teeth fall into the craters formed during previous bit rotations, severely affects the performance of roller cone rock bits. The tracking tendencies of tungsten carbide insert (TCI) bits are generally considered once the bit is built and tested, rather than during the design process. Once tracking is initiated, crater depth quickly reaches the full projection of the teeth, bringing the cone steel in contact with the rock. This tracking increases the contact area while reducing contact stresses beneath the inserts. Tracking increases the likelihood that neighboring rows of cutters will line up on the hole bottom, forcing the bit to rotate about a point other than its geometric center. This phenomenon is termed off-center rotation or forward whirl. Off-center rotation produces rings of uncut bottom and a further reduction in contact stresses. This article covers laboratory and field data used in the development and validation of a proprietary algorithm that determines the optimal tooth spacing to eliminate tracking. This study confirms that an algorithm can be applied effectively in the roller cone bit design process to improve coverage of the rock surface during drilling. In addition, these laboratory tests improve the understanding of a single gear-like wheel, a key to understanding total bit behavior.
- OSTI ID:
- 242274
- Journal Information:
- Oil and Gas Journal, Vol. 94, Issue 20; Other Information: PBD: 13 May 1996
- Country of Publication:
- United States
- Language:
- English
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