A master bushing is a critical component in rotary drilling that fits into the rotary table and transmits the rotary motion to the kelly bushing, ultimately turning the drill string.
Function and Purpose
The primary function of the master bushing is to:
- Accommodate Slips: The master bushing provides a landing platform for the slips. Slips are wedge-shaped devices that grip the drill pipe, casing, or tubing, allowing the drill string to be suspended in the wellbore.
- Drive the Kelly Bushing: The master bushing is designed to engage with and drive the kelly bushing.
- Transfer Rotary Motion: The rotary table's rotational force is transferred through the master bushing to the kelly bushing and then to the kelly, the topmost section of the drill string with a square or hexagonal cross-section. This rotation is what turns the drill bit at the bottom of the well.
Design and Operation
The master bushing is typically a heavy-duty, split circular device with a machined inner surface to accommodate different sized kelly bushings or slips. The split design allows it to be easily installed and removed from the rotary table. The inner surface can be customized to accommodate various inserts, which are used to handle different sizes of drill pipe or casing.
Types of Master Bushings
While the core function remains the same, master bushings come in different types depending on the drilling rig and the types of drilling operations being performed. Some common types include:
- Solid Master Bushings: These are one-piece bushings, offering high strength and rigidity.
- Split Master Bushings: As mentioned, these are split into two or more segments for easier handling and installation.
- Hinged Master Bushings: Similar to split bushings, but connected by hinges for convenience.
Importance in Drilling
The master bushing is essential for efficient and safe drilling operations. Its ability to securely hold the slips and efficiently transfer rotary motion directly impacts drilling speed and overall wellbore integrity. Properly maintained and appropriately sized master bushings are crucial for preventing downtime and ensuring a successful drilling project.
