Novel Selection Tool Enables Scientific Approach to Matched Assemblies

Barton, Steven (NOV Downhole Tools & Pumping) | Murdock, Andy (NOV Downhole Tools & Pumping) | Gee, Ryan (NOV Downhole Tools & Pumping)


Abstract Matching the drill bit to a directional motor assembly is critical to efficiently attaining the desired well trajectory. However, selecting the correct bit for the motor in a vertical application is just as vital. If the bit is too aggressive, it can stall the motor and significantly reduce the average rate of penetration (ROP). It will also increase the likelihood of premature failure of the elastomeric liner of the motor power section or twist off of internal motor components. If the bit is not aggressive enough, it will not make full use of the available motor power and the ROP will be sub-optimal. To ensure consistent and accurate matching of the bit to a specific downhole motor, an interactive, intranet tool was developed. This software incorporates logic regarding the configuration of the motor power section and assesses this against key characteristics of the drill bit including length, profile, gauge geometry, cutting structure, and secondary torque control components. The tool enables the user to first select the motor type and the key parameters from which the expected motor RPM, torque, and power are calculated. This information can then be utilized to identify the ideal bit design based on the four fundamental performance indices, derived from a sophisticated mathematical model. These indices describe the performance of the bit in terms of ROP, Stability, Durability and Steerability. They represent a scientific and accurate means to match the relative aggressivity of the bit to the torque output of the motor. Several case studies are documented which clearly demonstrate that matching the drill bits to motor power sections delivers greatly improved drilling efficiency and significantly lowered drilling cost. As a result, the latest generation of even-wall technology mud motors has been utilized to their full potential.

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