Abstract

As it is known to all, lift sub is a short drill string component that is temporarily connected to the top of a tool assembly that is to be lifted vertically, such as when running or retrieving a tool string.

The external profile on the upper section of the conventional lift sub is similar to that of the drill pipe, enabling the rig elevators to lift the assembled tool string safely. The conventional lift sub is made of one piece of the steel, and the bottleneck of this structure is: when the upper section is seated in the elevators, the lower part (thread section) is difficult to rotate while the drill collar is connected, which brings intensive labor force to makeup connections and run in hole. Drill collar is thick wall tubular with threaded connections, is an important component of a drill string that provides weight on bit for drilling. The drill collar, male on one end and female on the other, can be screwed together along with other downhole tools to make a bottom hole assembly (BHA). The more drill collars connected, the heavier the BHA is, the more difficult to rotate the string. Based on this, the rotatable lift sub is invented and applied; axial cylindrical roller bearings are adopted to make the lower part rotate with flexibility. After the upper section is seated in the elevator and then fixed together as the cause of weight, while the lower part can be rotated with the drill collar, which brings great convenience to the operation of makeup connections of drill collar and such downhole tools.

The successful field application of the rotatable lift sub has proven its advantages, with increased safety and efficiency.

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