| 摘要 |
A method for selecting a drilling motor for rotating a drill bit relative to a drill string made up of casing accounts for a tendency for the casing to elongate as the internal pressure increases. The increase in pressure in the casing string increases the weight on the drill bit, the amount of which may be calculated based on the size and type of the string of casing. The ratio of bit torque over the weight on the bit may be assumed to be a constant number based on empirical measurements or a theoretical model. The increase in the weight on the drill bit can be expressed in terms of the bit torque versus the casing pressure, which is a linear slope. This linear slope may be compared to the delivery torque of candidate motors.
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