Drill Pipe Connection Method

What is drill pipe?

Drill pipe is a steel pipe with a thread at the end, used to connect the surface equipment of the drilling rig to the drilling and grinding equipment or bottom hole device at the bottom of the drilling well. The purpose of the drill pipe is to transport drilling mud to the drill bit and to raise, lower or rotate the bottom hole device together with the drill bit. Drill pipe must be able to withstand tremendous internal and external pressure, twisting, bending and vibration.

Drill pipe joint:
The drill pipe joint is a component of the drill pipe, divided into a male joint and a female joint, which are connected to the two ends of the drill pipe body. In order to enhance the connection strength of the joint, the wall thickness of the pipe body needs to be increased at the joint. According to the method of thickening, it can be divided into three forms: internal thickening, external thickening, and internal and external thickening.

The buckle connection must meet three conditions:
① Equal size;
② Same thread type;
③ Matching of male and female buckles.

API 5DP Drill pipe Connection Method:

The API 5DP drill pipe connection method is a key factor affecting the overall performance of the drill string. It is mainly categorized into two types: API standard joints and high-performance special joints. The choice directly affects torsional strength, sealing, and fatigue life.

1）API standard drill pipe connection methods

According to the thread type drill pipe joints are divided into four types: IF（Internal flush connection); FH (Full hole connection)；REG (Regular connection)；NC (Numbered connection).

NC is a new series, gradually replacing all IF in the API standard and all FH connectors except 5 1/2" FH. There are several interchangeable with old API connectors, mainly NC50-2 3/8"IF, NC38-3 1/2"IF, NC40-4"FH, NC46-4"IF, NC50-4 1/2"IF.

1. Internal flush connection (IF)

Mainly used for external thickening drill pipe. Its characteristics are that the drill pipe has the same internal diameter throughout the body and small drilling fluid flow resistance; but the outer diameter is large and easy to wear.

2. Full hole connection (FH)

Mainly used for internal and external thickening Thick drill pipe. Its characteristic is that the drill pipe has two inner diameters, the drilling fluid flow resistance is greater than the inner flush type, but its outer diameter is smaller than the regular type.

3. Regular connection (REG)

Mainly used for internal thickened drill pipe, drill bit, and salvage tools. Its characteristic is that the inner diameter of the thickened inner diameter of the joint is smaller than the inner diameter of the pipe body, the drilling fluid flow resistance is large, and the relative flow resistance is the largest among the three buckle types, but the outer diameter is the smallest and the strength is greater. The above three types of joints all use V-type threads, but the buckle type, buckle distance, taper and size are very different.

4. Numbered connection (NC)

The digital series joint is the American national standard coarse thread series. It has now been adopted as an international standard by API. NC thread is also a V-thread. Some NC joints have the same pitch diameter, taper, pitch and thread length as the old API standard joints and can be used interchangeably.

2）High-performance special joint methods

1. Double-shouldered joint (such as XT57): Adds a secondary shoulder, increasing torsional resistance by 30%. It is the preferred choice for shale gas fracturing wells and resists vibration fatigue.
2. Metal sealing buckle (such as VAM TOP): Precision-ground metal surfaces create a gas-tight seal. Essential for deepwater drilling to prevent gas channeling.
3. Direct-connect (TLC): No couplings are required, and the drift diameter is increased by 15%. It reduces friction and reduces the risk of stuck pipe in horizontal wells.
4. Anti-fatigue joint: Optimizes stress distribution at the thread root.

Most oil drill pipe joints are in the form of external thickening or internal and external thickening. The outer diameter of the drill pipe joint is larger than the outer diameter of the pipe body. During the drilling process, it is constantly in contact and friction with the well wall or casing, causing wear. In order to avoid drilling accidents such as broken drill pipe and tripping caused by joint wear, a drill pipe joint anti-wear belt must be provided on the drill pipe female joint.

Drill pipe joint type and size matching:

The function of the connector:

As a key component for connecting drill pipes, joints play a very important role. The joints must not only be able to bear huge pressure and tension, but also have wear-resistant, corrosion-resistant properties.

There are many types of joints, among which the more common ones include threaded joints, reversible joints, non-torque joints, etc. These joints have their own characteristics and scope of application, and they need to be selected according to the operating conditions.

In addition to the function of the joint itself, the joint is often used for geological exploration and data collection, such as temperature measurement, pressure measurement, flow measurement, etc. These operations require the transmission of data through connectors and are critical to exploration and acquisition efforts.

How to connect kelly pipe and drill pipe?

1. Direct connection
Kelly pipe and drill pipe can be connected using direct connection. This method requires cleaning the surface of the kelly and drill pipe first to ensure the safety of the connection.
The advantage of direct connection is that it is simple and convenient to connect, avoids connection gaps, and can effectively reduce friction loss during rotation of the connection and resistance to sludge discharge. However, direct connection has shortcomings such as low connection strength and easy breakage. It is necessary to pay attention to the strength during connection and inspection after use.

2. Install interface connection
In addition to direct connection, you can also use the installation interface connection method. This method requires the drill pipe and kelly pipe to be installed with respective interfaces and connected through the interfaces.
The advantages of the installation interface connection are high connection strength, high efficiency, and easy replacement of connecting parts. However, installing interface connections requires more preparation work, including installing interfaces, inspecting interfaces, installing drill pipes, etc.

Whether it is direct connection or installation interface connection, you need to pay attention to the following usage precautions:
a. Before connection, the surface finish of the connecting parts and the circular runout error of the connecting parts should be checked.
b. When connecting, the drill pipe should be installed correctly and with appropriate strength, and should not be excessively loose or too tight.
c. Thorough cleaning should be carried out after connection to prevent mud from entering the connection holes.
d. During use, regularly check the wear degree of connecting parts and make necessary replacements.

In short, the connection method between kelly and drill pipe plays a vital role in the safe operation of drilling projects and drilling efficiency. According to actual needs and conditions, selecting appropriate connection methods and strengthening maintenance and inspection can effectively improve project efficiency and reduce risks.

Read more: Casing pipe VS Drill pipe or What types of oil drill pipes are there?