Highlights
- A Kelly bushing is a cylindrical metal sleeve that is inserted into the top of a drill string to provide a rotating connection between the drill string and the drill bit.
- The torque required to tighten a Kelly bushing will depend on the size of the Kelly bushing and the drilling application.
- They provide a rotating connection between the drill string and the drill bit, support the weight of the drill string, protect the drill string from wear, and create a fluid seal between the drill string and the wellbore.
A Kelly bushing is a cylindrical metal sleeve that is inserted into the top of a drill string to provide a rotating connection between the drill string and the drill bit. It is named after its inventor, John Kelly, who developed it in the early 1900s. Kelly bushings are used in a wide variety of drilling applications, including oil and gas exploration, water well drilling, and geothermal drilling.
Functions of a Kelly Bushing
The primary function of a Kelly bushing is to provide a rotating connection between the drill string and the drill bit. This allows the drill string to rotate the drill bit, which in turn breaks up the rock or soil being drilled. Kelly bushings also serve several other important functions, including:
- Providing a fluid seal: Kelly bushings create a fluid seal between the drill string and the drill bit. This prevents drilling fluid from leaking out of the drill string and into the wellbore.
- Supporting the weight of the drill string: Kelly bushings help to support the weight of the drill string. This prevents the drill string from buckling or collapsing under its own weight.
- Protecting the drill string from wear: Kelly bushings protect the drill string from wear and tear. This is especially important in abrasive drilling environments, such as those encountered in oil and gas exploration.
Types of Kelly Bushings
There are two main types of Kelly bushings:
- Fixed Kelly bushings: Fixed Kelly bushings are permanently attached to the top of the drill string. They are typically used in shallow drilling applications, where the drill string does not need to be rotated frequently.
- Rotary Kelly bushings: Rotary Kelly bushings can be rotated independently of the drill string. This allows the drill string to be rotated without rotating the Kelly bushing. Rotary Kelly bushings are typically used in deep drilling applications, where the drill string needs to be rotated frequently.
Materials Used in Kelly Bushings
Kelly bushings are typically made of high-strength steel alloys. These alloys are designed to withstand the harsh conditions encountered in drilling operations, including high temperatures, high pressures, and abrasive drilling fluids.
Kelly Bushing Sizes
Kelly bushings are available in a variety of sizes to accommodate different drill string diameters. The most common Kelly bushing sizes range from 2-3/8 inches to 6-5/8 inches in diameter.
Kelly Bushing Maintenance
Kelly bushings require regular maintenance to ensure that they are functioning properly. This maintenance includes:
- Inspecting the Kelly bushing for wear and tear: Kelly bushings should be inspected regularly for signs of wear and tear. Any damaged Kelly bushings should be replaced immediately.
- Lubricating the Kelly bushing: Kelly bushings should be lubricated regularly to prevent them from seizing up. The type of lubricant used will depend on the specific drilling application.
- Tightening the Kelly bushing: Kelly bushings should be tightened regularly to ensure that they are properly secured. The torque required to tighten a Kelly bushing will depend on the size of the Kelly bushing and the drilling application.
Kelly Bushing Replacement
Kelly bushings should be replaced when they become damaged or worn out. Damaged Kelly bushings can cause the drill string to buckle or collapse, which can lead to serious injuries or even death. Worn-out Kelly bushings can reduce the efficiency of the drilling operation and lead to increased downtime.
How to Choose the Right Kelly Bushing
The following factors should be considered when choosing a Kelly bushing:
- The size of the drill string: The Kelly bushing must be compatible with the size of the drill string.
- The type of drilling application: The type of drilling application will determine the type of Kelly bushing that is required.
- The drilling environment: The drilling environment will determine the materials that are used in the Kelly bushing.
The Bottom Line: Understanding the Importance of Kelly Bushings
Kelly bushings are critical components of drilling operations. They provide a rotating connection between the drill string and the drill bit, support the weight of the drill string, protect the drill string from wear, and create a fluid seal between the drill string and the wellbore. By understanding the functions, types, and maintenance of Kelly bushings, drilling operators can ensure that their drilling operations are safe and efficient.
Frequently Asked Questions
Q: What is the difference between a fixed Kelly bushing and a rotary Kelly bushing?
A: Fixed Kelly bushings are permanently attached to the top of the drill string, while rotary Kelly bushings can be rotated independently of the drill string.
Q: What are Kelly bushings made of?
A: Kelly bushings are typically made of high-strength steel alloys.
Q: How often should Kelly bushings be inspected?
A: Kelly bushings should be inspected regularly for signs of wear and tear. The frequency of inspection will depend on the drilling application and the condition of the Kelly bushing.
Q: How often should Kelly bushings be lubricated?
A: Kelly bushings should be lubricated regularly to prevent them from seizing up. The frequency of lubrication will depend on the drilling application and the type of lubricant used.
Q: How often should Kelly bushings be tightened?
A: Kelly bushings should be tightened regularly to ensure that they are properly secured. The torque required to tighten a Kelly bushing will depend on the size of the Kelly bushing and the drilling application.