| 摘要 |
<p>Drill string assemblies, bottom hole assemblies (BHAs), and powertrains for a BHA in a drill string are presented herein. A BHA for use in a drill string to drill boreholes in an earth formation is disclosed. The BHA includes a housing, a drill bit rotatably coupled to the housing, and a fluidly driven motor assembly, such as a positive displacement motor (PDM). The PDM assembly includes a drive shaft to output rotational drive forces generated by the PDM. Also included is a differential gear set with a first gear member coupled to the drive shaft, a second gear member intermeshing the first gear member with the housing, and a third gear member coupled to the drill bit. The differential gear set transmits the rotational drive forces from the drive shaft to the drill bit and rotates the drill bit at a speed greater than the speed of the PDM assembly.</p> |
