What is Oil Drill Pipe?

Oil drill pipe is an indispensable key component in oil and gas drilling engineering. It is a hollow steel pipe used to connect the drilling rig's surface equipment to the drill bit at the bottom of the well. It serves as a channel for drilling fluid circulation and is responsible for transmitting torque and tension to the bottom-hole tools. Drill pipe must possess high strength, good toughness, fatigue resistance, and corrosion resistance to cope with the complex downhole environment.

Drill pipe withstands enormous axial tensile forces, torque, internal and external pressure differentials, bending, and vibration during drilling. Therefore, materials, heat treatment, manufacturing precision, and joint design must strictly comply with international standards (such as API SPEC 5D and API SPEC 7-1).

Main Functions of Oil Drill Pipe

1. Power Transmission

Transmits the torque of the drilling rig spindle to the drill bit at the bottom of the well, causing the drill bit to rotate and break up the formation.

2. Drilling Fluid Delivery

Drilling fluid flows from the surface through the drill pipe to the drill bit, used to cool the drill bit, carry cuttings, and balance bottom-hole pressure.

3. Transferring Drill Pressure

Pressure is transferred to the drill bit through the weight of the drill string itself or by applying additional drill pressure to improve drilling efficiency.

4. Connecting Function

Tools such as kelly pipe, standard drill pipe, heavy weight drill pipe and drill collars are reliably connected to form a complete drill string.

Material Grades of Oil Drill Pipe

According to API SPEC 5D standard, common material grades for oil drill pipes include E75, X95, G105, and S135.

Structure of Oil Drill Pipe

Oil drill pipe mainly consists of three parts:

1. Pipe Body

Made of high-strength seamless steel pipe, with a wall thickness of generally 9–11 mm, it is the main body of the drill pipe.

2. Tool Joint

Made of alloy steel forgings, connected to the pipe body by friction welding or inertia welding. The joint is thicker and stronger than the pipe body to withstand torque and wear.

3. Welded Zone and Upset Section

Oil drill pipe is made of rolled seamless steel pipe. To enhance joint strength, both ends of the drill pipe are thickened.

Thickening methods include:

Internal Upset (IU)

External Upset (EU)

Combined Internal and External Upset (IEU)

The length of the thickened transition section is generally 20–130 mm, which can improve the fatigue life of the connection by 30–50%.

Oil Drill Pipe Lengths

Range 1: 5.49–6.71 m, shorter, commonly used for well workovers or special wells;

Range 2: 8.23–9.75 m, most common, approximately 9 meters/pipe;

Range 3: 12.19–13.72 m, commonly used in deep wells or offshore drilling.

Classification of Oil Drill Pipe

Oil drill pipe is classified into kelly pipe, ordinary drill pipe, and heavy weight drill pipe.

The connection sequence is: 1 kelly pipe + n standard drill pipes (determined by well depth) + n heavy weight drill pipes (determined by drill string assembly design).

Based on thread type, drill pipe joints are divided into four types: IF, FH, REG, and NC.

1. Kelly Pipe

The kelly pipe is located at the top of the drill string, usually square or hexagonal, and plays a crucial role in the drilling process.

Function of The Kelly Pipe:

During drilling, the kelly pipe, in conjunction with the bushing and rotating bushing, transmits the surface rotational torque to the drill pipe, thereby driving the drill string and drill bit.

It bears the weight of the entire drill string.

It serves as a channel for drilling fluid circulation.

Structure of The Kelly Pipe:

The kelly pipe consists of upper and lower joints and a pipe body.

The pipe body is usually square or hexagonal (square is more common in oil drilling).

2. Standard Drill Pipe

Function of The Standard Drill Pipe:

The drill pipe is a basic component of the drill string.

Its main functions are to transmit torque and deliver drilling fluid, and its gradually elongating characteristic allows for continuous wellbore deepening.

Standard Drill Pipe Structure:

Drill pipe mainly consists of two parts: the drill pipe body and the drill pipe joint.

The body, as the main structure of the drill pipe, provides primary support and transmits power.

The joint plays a crucial role in connecting multiple drill pipe sections to form a continuous drill string.

3. Heavy Weight Drill Pipe (HWDP)

Heavy weight drill pipe is similar to oil drill pipe, also a hollow steel column approximately 10 meters in length. However, each section weighs more than oil drill pipe, and its wall thickness is two to three times that of oil drill pipe.

Functions of Heavy Weight Drill Pipe:

Heavy weight drill pipe is a downhole tool used to add weight to drilling platforms.

It is typically installed between the drill pipe and drill collars, transmitting power and applying pressure to the drill bit.

It can prevent fatigue damage caused by changes in the drill string cross-section and can replace some drill collars.

Its simple suspension method makes tripping operations more convenient and time-saving.

Heavy Weight Drill Pipe Structure:

Heavy weight drill pipe features extended joints, increased wall thickness, and externally thickened sections.

Carbide-coated surfaces extend its service life.

Oil Drill Pipe Standards

API SPEC 5D (Seamless drill pipe standard)

API SPEC 7-1 (Drill string connector standard)

ISO 10424-1 / ISO 15546 (International equivalent standard)

NS-1™ / DS-1™ (Third-party certification standard, commonly used in the North Sea and North American markets)

FAQ

1. What are The Common Specifications for Oil Drill Pipe?

According to API SPEC 5D standard, common sizes: 2 3/8" drill pipe, 2 7/8" drill pipe, 3 1/2" drill pipe, 4" drill pipe, 4 1/2" drill pipe, 5" drill pipe, and 5 1/2" drill pipe.

2. What is The Difference Between Oil Drill Pipe and Drill Collars?

Drill pipe is primarily used to transmit torque and deliver drilling fluid; drill collars are primarily used to apply drilling pressure and maintain wellbore stability; they differ in weight, diameter, and function.