In oil drilling equipment, the Top Drive is a device installed at the upper section of the derrick. It directly rotates the drill string from the top and feeds it downward along a dedicated guide rail to perform various drilling operations. The internationally recognized full term is Top Drive Drilling System, abbreviated as TDS.

The top drive system primarily consists of the swivel-drilling motor assembly, motor bracket/guide dolly assembly, drill pipe make-up and break-out device, compensation system, cooling system, TDS control system, and optional auxiliary equipment. Among these, the drilling motor, gearbox, integrated swivel, and compensator are the core components.

Key Advantages:

• Time-saving during pipe connection: Since it enables stand drilling, it is not limited by kelly length and avoids the frequent need to add single joints as drilling progresses.

• Backreaming capability: It allows for backreaming during tripping out without additional tripping time, reducing the risk of stuck pipe.

• Reduced stuck pipe risk while tripping in: The system allows for quick pipe connections and backreaming during running in hole.

• Safer connections: It uses motor-driven make-up, providing smooth and consistent torque, preventing over- or under-torquing and protecting equipment.

Working Principle

1. Rotational Power Transmission

The top drive’s core is the drilling motor, typically an AC variable frequency motor or a hydraulic motor. When activated, the motor generates rotational power, which is transmitted through a gearbox to the main shaft in the swivel-drilling motor assembly. This main shaft is connected to the drill pipe, driving it to rotate at high speed. This rotation provides the necessary torque to break the rock and achieve drilling progress.

2. Axial Feed Motion

Mounted on a dedicated guide rail at the top of the derrick, the top drive can move vertically via a compensation system and drive mechanism. During drilling, the system feeds the drill pipe downward with controlled speed and pressure, ensuring continuous contact between the drill bit and formation. This feed motion enables efficient cutting and debris removal.

3. Drill Pipe Connection and Disconnection

The top drive is equipped with a make-up and break-out sub-assembly for quick connection and disconnection of drill pipe. When a new joint is needed, the sub-assembly aligns and torques the new pipe to the existing string. For tripping out or bit changes, the system loosens the connection, enabling easy removal of the drill pipe.

4. Drilling Fluid Circulation

The swivel in the swivel-drilling motor assembly is an essential part of the mud circulation system. Drilling fluid is pumped from the mud pump through high-pressure lines to the swivel, passes through internal channels into the drill pipe, flows downward, and exits through the bit nozzles. This circulation system carries cuttings to the surface, cools the bit, lubricates the pipe, and stabilizes the wellbore.