A Kelly bushing is a mechanical device that transmits torque from the rotary table to the kelly, which is a hollow square or hexagonal pipe that is used to drill oil and gas wells. The kelly bushing is a critical component of the drilling rig, and it must be properly designed and maintained to ensure the safety and efficiency of the drilling operation.
Function
The Kelly bushing performs two main functions:
- Transmits torque from the rotary table to the kelly: The rotary table is a large, rotating platform that is powered by the drilling rig's engine. The kelly bushing is attached to the rotary table and has a square or hexagonal inner surface that matches the outer surface of the kelly. As the rotary table rotates, the kelly bushing turns the kelly, which in turn rotates the drill string.
- Allows the kelly to move vertically: The Kelly bushing is designed to allow the kelly to move up and down freely as the drill string is lowered into the well and raised to make connections. This is accomplished by using rollers or other mechanisms to reduce friction between the kelly bushing and the kelly.
Design
Kelly bushings are typically made of high-strength steel and are designed to withstand the high torques and forces that are generated during drilling. The inner surface of the kelly bushing is hardened to resist wear and tear. The kelly bushing is also typically equipped with a number of safety features, such as a kelly cock valve to prevent backflow of drilling mud and a safety sub to prevent the kelly from becoming stuck in the wellbore.
Types
There are two main types of kelly bushings:
- Square kelly bushings: Square kelly bushings are the most common type of kelly bushing. They have a square inner surface that matches the square outer surface of the kelly.
- Hexagonal kelly bushings: Hexagonal kelly bushings are less common than square kelly bushings. They have a hexagonal inner surface that matches the hexagonal outer surface of the kelly.
Installation and maintenance
Kelly bushings are typically installed on the rotary table using a crane. Once the kelly bushing is installed, it is important to regularly inspect it for wear and tear. The kelly bushing should also be lubricated regularly to reduce friction and wear.
Safety
Kelly bushings are critical safety components of drilling rigs. It is important to ensure that kelly bushings are properly designed, installed, and maintained to prevent accidents. Some common safety hazards associated with kelly bushings include:
- Kelly bushing failure: If a kelly bushing fails, the kelly can become stuck in the wellbore, which can lead to a serious drilling accident.
- Kelly bushing kickback: If the kelly bushing is not properly lubricated, it can cause the kelly to kick back, which can injure personnel or damage equipment.
- Kelly bushing fire: If the kelly bushing overheats, it can start a fire on the drilling rig.
Conclusion
Kelly bushings are essential components of drilling rigs. They play a critical role in transmitting torque from the rotary table to the kelly and allowing the kelly to move vertically. Kelly bushings must be properly designed, installed, and maintained to ensure the safety and efficiency of the drilling operation.
