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What is Oil Drill Pipe? What are the Steel Grades and Materials of Oil Drill Pipes?

Date:2024-02-29    keywords: oil drill pipe, oil drill pipe steel grades and materials, drill pipe type and length,specification
What is oil drill pipe?

Oil drill pipe is used for oil well drilling. Drill pipe is characterized by thin wall and light weight per unit length. It mainly provides mud passage and transmits pulling force and torque. (There is also a type of oil drill jack: thick wall, heavy weight per unit length, mainly providing mud passage, transmitting pulling force and torque and providing drilling weight for the drill bit.)

What are the steel grades of oil drill pipes?

Common oil drill pipe steel grades include E75, X95, G105, and S135.

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. In the process of oil and gas extraction and refining, drill pipe can be used multiple times. Drill pipe is divided into three categories: kelly, drill pipe and weighted drill pipe. The connection sequence is kelly (1 piece) + drill pipe (n pieces, determined by the well depth) + weighted drill pipe (n pieces, determined by the design of the drill tool assembly). It introduces in detail the classification of drill pipes, drill pipe joints, drill pipe specifications, and the steel grade and strength of drill pipes.

API standard E75 to S135 steel grades, series of oil drill pipes with outer diameters from 2 3/8″ to 6 5/8″, as well as double shoulder joint drill pipes with high torsional performance and special steel for sour oil wells Grade BNK C95S drill pipe. It is mainly suitable for the construction of deep wells, horizontal wells and extended reach wells in the process of oil and gas exploration and development.

drill pipe

Drill pipe material selection:

Since horizontal directional drilling passes through various strata, the drill pipe faces relatively large pressure, friction and other factors, and needs to have high strength, good toughness, corrosion resistance and wear resistance. The following are several common drill pipe materials and their advantages and disadvantages.

1. High strength alloy steel
This is one of the most commonly used drill pipe materials. It has high strength and toughness and can withstand great tension and pressure. Moreover, this kind of steel has a long life and is not easy to rust and wear. However, the price of high-strength alloy steel is relatively high, which is not conducive to cost savings. Additionally, if it is not properly maintained, problems such as embrittlement and deterioration can occur.

2. Manganese steel
Manganese steel materials perform well in terms of corrosion resistance, wear resistance and toughness. Due to its relatively low strength, the structure needs to be strengthened during design to ensure its tension and compression. However, this type of steel is relatively cheap compared to other steel types. Note that manganese steel may deform during drilling.

3. Stainless steel
In horizontal drilling rig mud, stainless steel exhibits good corrosion resistance and can maintain the integrity of the drill pipe. However, the relatively low hardness of stainless steel makes it unsuitable for drilling operations that require use under strong vibration. Additionally, stainless steel has limited chemical resistance to corrosive slurries.

4. Titanium alloy
Titanium alloy materials have excellent performance in terms of oxidation resistance and corrosion resistance. Due to its low density and relatively light weight, it is ideal for horizontal drilling at greater depths. However, titanium alloys are more difficult to manufacture and more expensive.

Oil drill pipe types and their differences?

Oil drill pipe is an important tool in oil drilling and is mainly used for drilling and drilling operations. According to their uses and characteristics, common oil drill pipe types and their differences are as follows:

1. Drilling and workover riser (Drill Pipe): a pipe used to connect drilling tools and drill bits. It is usually made of non-magnetic steel to prevent magnetism from interfering with logging and geomagnetic exploration. According to different needs, it can be divided into standard drill pipe and high-strength drill pipe.
2. Drill Collar: used to connect two sections of drill pipe to increase the total drill pipe weight, enhance drilling and stabilize the wellbore. According to the shape and use, it can be divided into straight drill string and turbulent drill string.
3. Anchor (Stabilizer): used to stabilize the well wall during drilling and prevent well wall collapse and diameter expansion. According to the form and function principle of stabilizing the well wall, it can be divided into cutting type stabilizer and sliding type stabilizer.
4. Magnetic pressure change detector (MWD) in the drill string: By installing a measuring device in the drill string, downhole drilling parameters, including pressure, temperature, vibration, etc., can be monitored in real time to guide drilling operations. These oil drill pipes play different roles in the oil drilling process and are suitable for different working conditions and needs. Based on the well depth, formation properties and work requirements, drilling engineers will select the appropriate oil drill pipe model to complete the drilling task. 

Drill pipe is divided into three categories: kelly, drill pipe and weighted drill pipe. The connection sequence is kelly (1 piece) + drill pipe (n pieces, determined by the well depth) + weighted drill pipe (n pieces, determined by the design of the drill tool assembly).

1. Kelly: The kelly is located at the uppermost end of the drill string and comes in two types: square and hexagonal.
The function of the kelly: 

① When drilling, the kelly cooperates with the center filler and the turntable center filler to transmit the ground rotation torque to the drill pipe to drive the drill string and drill bit to rotate;
② Bear the full weight of the drill string;
③Channel for drilling fluid circulation.

The structure of kelly pipe:
Kelly pipe consists of upper and lower joints and pipe body parts. The pipe body part has two structures: square or hexagonal (most oil drilling wells have a square structure); the upper joint has a left-hand female thread (reverse buckle), which is connected to the faucet. The left-hand female thread prevents reverse buckle during the rotation; the lower joint It is a right-hand male thread and is connected to the drill pipe. When working, the upper end of the kelly is always above the turntable surface, and the lower part is below the turntable surface.

2. Drill pipe
The role of drill pipe: Drill pipe is the basic component of the drill string. Its main function is to transmit torque and transport drilling fluid, and to continuously deepen the wellbore by gradually lengthening the drill pipe. Therefore, drill pipe plays a very important role in oil drilling.

Drill pipe structure:
The drill pipe is made of stainless steel pipe, with a wall thickness of generally 9 to 11 mm; it consists of a drill pipe body and a drill pipe joint. The pipe body and joint are butt welded together by friction welding.

3. Weighted drill pipe
Weighted drill pipe is similar to oil drill pipe. It is also a hollow steel column with a length of about 10 meters. However, a single piece of weight is heavier than an oil drill pipe, and its wall thickness is 2 to 3 times that of a drill pipe. The weighted drill pipe is connected between the drill pipe and the drill collar to prevent fatigue damage due to changes in the drill string cross-section. It can also replace part of the role of drill collars, but its suspension is simple and the tripping operation is convenient, which can save tripping time.

Drill pipe joint classification:
The drill pipe joint is an integral part of the drill pipe. It is divided into male and female joints and is connected to both 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 part. According to the thickening method, it can be divided into three forms: internal thickening, external thickening, and internal and external thickening. The joints are threaded (threaded) to connect individual drill pipes. The threads of the drill pipe joints are tapered pipe threads with a sealing shoulder. The shoulder surface is tightened to seal, and the thread only serves to connect. Different thickening methods have different thread buckle types of corresponding joints.

Threaded drill pipe joints are divided into four types: internal flat (IF), through hole (FH), regular (REG), and digital (NC).

Buckle connection conditions:
There are three conditions that must be met for a buckle connection:
①The dimensions are equal;
②The thread type is the same;
③The male and female buckles match.

Drill pipe joint buckle type:
Internal flat type: mainly used for externally thickened drill pipes. Its characteristic is that the inner diameter of the drill pipe is the same, and the drilling fluid flow resistance is small; but the outer diameter is larger and easy to wear. Through-hole type: Mainly used for thickening drill pipe inside and outside. Its characteristic is that the drill pipe has two inner diameters. The drilling fluid flow resistance is greater than the inner flat type, but its outer diameter is smaller than the regular type. Formal type: Mainly used for internally thickened drill pipes, drill bits, and fishing tools. Its characteristic is that the inner diameter of the thickened part of the joint is smaller than the inner diameter of the pipe, and the drilling fluid flow resistance is large. Among the three buckle types, the relative flow resistance is the largest, but the outer diameter is the smallest and the strength is greater. The above three types of joints all use V-shaped threads, but the buckle type, buckle pitch, taper and size are very different.

Digital (NC) series connectors are American National Standard coarse thread series. It has been adopted by API as an international standard. NC threads are also V-shaped threads. Some NC-type joints have the same pitch diameter, taper, pitch and thread length as the old API standard joints and can be used interchangeably.

Most oil drill pipe joints adopt 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. During the drilling process, it constantly contacts and rubs with the well wall or casing, causing wear. In order to avoid joint wear and cause drill breakage To prevent drilling accidents such as rod and tripping, a drill pipe joint anti-wear belt must be installed on the drill pipe female joint.

Drill pipe specification classification:

According to the regulations of the American Petroleum Institute (API), drill pipes are divided into three categories according to length (L): Category 1: 5.486 to 6.706m (18 to 22ft); Category 2 (commonly used): 8.230 -9.144m (27-30ft); Category III: 11.582 to 13.716m (38 to 45ft). Drill pipe can also be classified by outer diameter size. Commonly used drill pipe sizes (D): 88.9, 114.3, 127mm (customarily expressed in imperial dimensions: 3 1/2″4 ½″5″).

Steel grade strength of drill pipe:

The steel grade of drill pipe refers to the grade of drill pipe steel, which is determined by the yield strength of drill pipe steel. API (American Petroleum Institute) divides drill pipe steel grades into five grades: D, E, 95(X), 105(G), and 135(S). The higher the drill pipe steel grade, the greater the yield strength of the pipe and the greater the various strengths of the drill pipe. In the strength design of the drill string, it is recommended to increase the strength of the drill string by increasing the steel grade instead of increasing the wall thickness.

What is the length of oil drill pipe?

The length of oil drill pipe is generally about 9 meters and the diameter is 5 inches. In addition, oil drill pipes are all rolled seamless steel pipes. In order to strengthen the connection strength between the pipe body and the joint, both ends of the drill pipe body are roughened and thickened. The thickening form is divided into internal thickening and external thickening according to API standards. There are three types: internal thickening and external thickening. The thickened transition section is generally 20~65mm long, and the longest can be 120~130mm.

Read more: Common Drill Pipe Connection

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