The Three Components of the Drill String
Drill pipes are classified into three categories: kelly drill pipe, drill pipe, and heavy weight drill pipe. The connection order is: kelly drill pipe at the top, then drill pipe sections determined by well depth, then heavy weight drill pipe sections determined by drill string assembly design.
Kelly Drill Pipe
The kelly is located at the top of the drill string and comes in square and hexagonal forms. During drilling, the kelly, in conjunction with the center filler and rotary table, transmits the surface rotational torque to the drill pipe, driving the drill string and drill bit to rotate; it bears the entire weight of the drill string; and it serves as the channel for drilling fluid circulation. The kelly consists of upper and lower connectors and the body: the upper connector has a left-hand female thread connecting to the swivel, preventing back-threading during rotation, and the lower connector has a right-hand male thread connecting to the drill pipe.
Drill Pipe
Drill pipe is the basic component of the drill string. Its main functions are to transmit torque and transport drilling fluid, and to continuously deepen the wellbore by gradually lengthening the string. It is made of seamless steel tubing with a wall thickness of generally 9 to 11 mm, consisting of the pipe body and tool joints, which are butt-welded by friction welding.
Heavy Weight Drill Pipe
The heavy weight drill pipe is a hollow steel column, approximately 10 meters in length, similar to regular drill pipe but with a wall thickness 2 to 3 times greater and a heavier weight per pipe. It is connected between the drill pipe and the drill collar to prevent fatigue damage caused by changes in the cross section of the drill string and can replace part of the function of the drill collar. Its suspension is simple and tripping is convenient, saving tripping time.
Drill String Design Considerations
The combination of kelly, drill pipe, and heavy weight drill pipe is selected according to well depth, torque requirements, and fatigue considerations. Grades are chosen by minimum yield strength, and the transition sections between different stiffness components are managed to prevent stress concentration.
Frequently Asked Questions
Q: What are the three types of drill pipe?
A: Kelly, drill pipe, and heavy weight drill pipe.
Q: What is the kelly used for?
A: Transmitting rotary torque from the surface, bearing string weight, and carrying drilling fluid.
Q: What is the wall thickness of drill pipe?
A: Generally 9 to 11 mm.
Q: Why use heavy weight drill pipe?
A: To prevent fatigue damage at cross-section changes and replace part of the drill collar function.
Q: How are joints attached?
A: Tool joints are butt-welded to the tube by friction welding.
Q: What is the length of heavy weight pipe?
A: Approximately 10 meters.
For drill pipe quotations with your required grade and size, contact our sales team.
