Applications of Drill Pipe in Oil Exploration and Development

Drill pipe is one of the most important tools in oil drilling operations. Its core function is to connect the drilling rig's surface equipment with the bottomhole drilling tool (such as the drill bit), transmit torque and drilling fluid, and withstand complex loads. Therefore, drill pipe is indispensable for almost all rotary drilling operations. Drill pipe has a wide range of applications in oil exploration and development. The following is a detailed classification of its main applications:

1) Classification by Drilling Type

1. Conventional Oilfield Drilling
This is the most common application. Drill pipe is used in most conventional oilfield drilling operations, transmitting torque and transporting drilling fluid to deepen the wellbore. On land or offshore platforms, medium to ultra-deep wells are drilled to recover oil and natural gas. This is the most common and fundamental application of drill pipe.

Material Selection: Steel pipe drill pipe is commonly used in conventional oilfield drilling. This type of drill pipe is made of seamless steel pipe and offers high strength and rigidity.

2. Deep and Ultra-Deep Well Drilling
Drilling operations exceeding 4,500 meters (deep wells) or 6,000 meters (ultra-deep wells) place extremely high demands on drill pipe, requiring the use of high-strength steel grades (such as S-135 and V-150) and thick-walled drill pipe to withstand the enormous tensile loads, torque, and high downhole pressure.

3. Directional, Horizontal, and Extended Reach Drilling
These non-vertical wells place extremely stringent demands on drill pipe's fatigue resistance (especially bending fatigue) and torque resistance. The high-speed rotation of drill pipe in curved wellbores exposes it to alternating stresses, making it susceptible to fatigue failure. This often requires the use of higher-performance drill pipe, with weighted drill pipe used in critical areas to increase weight on bit and reduce fatigue.

4. Underbalanced Drilling
In this type of drilling, bottomhole pressure is lower than formation pressure. The drill pipe must not only withstand normal loads but also possess excellent sealing properties to control wellhead pressure. High-performance drill pipe with specialized threaded joints is sometimes used.

5. Geological Exploration/Scientific Drilling Wells
Used for mineral resource exploration or crustal research. These wells are typically very deep, and the drill pipe requirements are similar to those for ultra-deep oil and gas wells.

2) Classification by Drilling Environment

1. Onshore Drilling
The environment is relatively mild, but may face varying climates, such as high and low temperatures, deserts, and Gobi Deserts. The drill pipe must withstand common corrosion and wear.

2. Offshore Drilling

Shallow-water drilling uses jack-up drilling platforms. The operating conditions are similar to those onshore, but the corrosive environment is more severe (marine atmosphere, seawater).

Deep-sea/Ultra-deep-sea drilling uses semi-submersible platforms or drillships. This is the ultimate test of drill pipe performance. In addition to withstanding the additional weight and pressure of immense water depths (thousands of meters), it must also withstand harsh sea conditions (waves, currents), and low temperatures. The drill pipe's strength, toughness, fatigue resistance, and corrosion resistance are all top-tier requirements.

3. Wells in Harsh and Complex Environments
Deep Well Operations: In deep well operations where drill pipe requires frequent addition and removal, auger drill pipe offers distinct advantages. Auger drill pipe is connected together using threaded connections, making it easy to operate.

High-Temperature, High-Pressure Environments: High temperatures downhole reduce the strength of steel, and high pressures challenge sealing. Special drill pipe materials that can withstand high temperatures while maintaining strength are essential.

Hydrogen Sulfide (H₂S) Wells: H₂S can cause hydrogen-induced cracking and sulfide stress corrosion cracking in drill pipe steel, which are extremely dangerous. Sulfur-resistant drill pipe (such as SM-SQ grades that meet API Spec 5DP) must be used. Its steel undergoes special treatment and has a strictly controlled hardness.

3) Classification by Drill Pipe Function and Position in the Drill String

Kelly Pipe: Located at the top of the drill string, it directly interfaces with the drill rig's rotary table, transmitting surface rotation and torque to the entire drill string. Suitable for all drilling operations requiring drill string rotation.

Conventional Drill Pipe: Consists of the main body of the drill string and is the most numerous. Suitable for all applications involving torque transmission, drilling fluid delivery, and extending well depth.

Heavy Weight Drill Pipe (HWDP): Its wall thickness is 2-3 times thicker than conventional drill pipe, resulting in greater weight and improved rigidity. It is typically placed in the middle of the drill string (between the drill pipe and the drill collar) to serve as a transition, effectively reducing fatigue damage within the drill string and providing some weight on bit (WOB). It is particularly suitable for directional, horizontal, and deep wells.

Drill Collar: Its wall thickness is the thickest and its weight is the heaviest. It provides WOB and maintains the stability of the lower drill string. Although not called "drill pipe," it is a key component of the drill string. It is suitable for all drilling operations requiring WOB on the drill bit.

4) Special Drilling Operations

Horizontal and Curved Wells: Wireline Drill Pipe is more suitable for horizontal and curved well operations. Wireline Drill Pipe is constructed from multiple strands of steel wire, is lightweight, and offers high adaptability.
Geological Exploration: Needle Valve Drill Pipe, with a needle valve at the bottom connector, controls gas pressure and flow at the bottomhole and is suitable for exploratory wells and geological exploration.

5) Drill Pipe Assembly Applications

Drill String Components: Oil drill pipe is a crucial component of the drill string and is typically used with a drill bit, drill collar, stabilizer, specialized joints, and kelly pipe.

Connection Order: During the drilling process, the drill pipe connection order is typically one kelly pipe + n drill pipes (determined by the well depth) + heavy weight drill pipe (n, determined by the drill assembly design).

6) Scientific Research and Underground Construction

Scientific Research: The working principles of drill pipe are also crucial in scientific research. By using drill pipe to penetrate underground, samples and data can be obtained, significantly aiding research in fields such as geology and climatology.

Underground Construction: In urban infrastructure construction, the use of drill pipe can avoid surface damage and enable more precise layout of underground facilities, such as pipelines and tunnels.

What is the difference between oil drill pipe and casing pipe in practical application?

Oil drill pipe and casing pipe are two completely different types of pipe with completely different functions and designs.

Drill pipe is a tool, the "drive shaft" and "highway" of the drilling process, used repeatedly during the drilling process.
Casing pipe is the foundational structure, the "skeleton" and "protective wall" of the well, and remains permanently in the well after drilling is completed.

Cooperative Working Scenarios:
During the construction of a well, the two work together:

First, a section of the well is drilled using the drill pipe and the drill bit.
Then, the drill pipe and drill bit are pulled out, and casing is lowered into the newly drilled section. Cement is injected into the casing to secure it.
A smaller drill bit is then used to continue drilling from within this casing, and the drill pipe is put into action again.
This process is repeated, like Russian nesting dolls, with smaller casing layers being lowered until the target depth is reached.

Drill pipe is a dynamic, retrievable drilling tool, while casing is a static, permanent wellbore structural material. They serve different purposes at different stages, ensuring the smooth progress of drilling operations and the long-term safety of oil and gas wells. Click here to learn more about the Applications of Oil Casing.

Conclusion:

Oil drill pipe has a wide range of applications in oil exploration and development, playing an important role in fields ranging from conventional oilfield drilling to specialized drilling operations under complex geological conditions, scientific research, and underground construction. Its application can be further categorized based on drilling type, depth, environment, and technical requirements.

Read more: API 5DP Drill Pipe Size and Specification or Drill Collar vs Drill Pipe