Cause analysis and solution of drill pipe failure

Date:2024-06-21Tags:drill pipe, pipe, Oil, casing and tubing, drill

Analysis of the causes of drill pipe failure

Drill pipes may fail at any part during the drilling process, leading to serious consequences or even scrapping. According to statistics, about five to six hundred drill pipe accidents occur in various oil fields in China every year, causing huge economic losses. With the depletion of shallow resources, the drilling of deep and ultra-deep wells has become more common, and the safety and reliability of drill pipes is particularly prominent. Drill pipe failure is generally manifested as body fracture and puncture, failure of drill pipe threads, etc. The reasons are generally caused by the following factors: basic mechanical working conditions of drill pipes during drilling, combination of drilling tools and drilling technology, regularity of parallel diameters, eccentric wear, thread sealing grease, drilling fluid, drill pipe structure and materials, formation factors, and internal corrosive media, etc. The interaction of the above factors leads to drill pipe failure.


The main reasons include the following aspects:

Basic mechanical working conditions: The drill pipe works in a narrow wellbore filled with drilling fluid, and is subjected to loads such as compression, bending, torsion, and hydraulic forces. Especially in large-displacement directional wells and horizontal wells, the composite stress is extremely large, which can easily lead to fatigue microcracks. Once the crack expands to a critical size, the drill pipe will break.

 drill pipe

The drill pipe will break if the drill bit is too small.

Drilling tool assembly and drilling technology: The drilling tool assembly determines the natural vibration frequency of the drill pipe. Resonance will add additional stress on the basis of the original fatigue stress, accelerating the failure of the drill pipe. Using long-lasting screw drill pipe to replace the rotary table drilling directional well and horizontal well drilling technology can reduce the degree of fatigue.

Vibration, bending and wear

When the drill string reaches the critical speed, the drill pipe will vibrate, which often causes bending, excessive wear, rapid damage and fatigue failure of the drill pipe. It is especially unfavorable when two types of vibration (wave node vibration and spring pendulum vibration) of the drill pipe coincide. The critical speed varies with the length of the drill tool, the size of the drill tool, the size of the drill collar and the size of the wellbore.

Tensile failure

Tensile failure often occurs when pulling up a stuck drill pipe. When the pulling force exceeds the yield point, a "neck" deformation will occur at the weakest part or the smallest section of the drill pipe wall. If the pulling force exceeds the ultimate strength just now, the drill pipe will be broken. Tensile failure usually occurs at the upper part of the drill string. This is because the upper drill bit has to bear both pressure and the weight of the drill string.

Drill pipe fatigue

Drill pipes will fatigue and crack due to continuous rotation and vibration. Especially in long-term high-intensity drilling operations, the degree of fatigue will be more serious. When the stress inside the drill pipe exceeds its bearing capacity, fatigue cracking will occur, resulting in the breakage of the drill pipe.

Problems with the design of the broken section area

During drilling operations, welded drill pipes are required. If the connection design is unreasonable or the welding quality is poor, cracks and defects are likely to occur in the broken section area, which will cause the broken section area to be difficult to control and remove during drilling. Improper design of the broken section area, such as the assembly of unsuitable connectors, can also cause the drill pipe to break.

Drilling parameter setting issues

During the drilling process, if the drill pipe is not properly pressurized or pulled, it may cause slight deformation of the drill pipe and uneven internal stress distribution, leading to fatigue fracture. At the same time, if the drilling parameters are set unreasonably, such as setting the drill bit speed too fast or the drilling pressure too high, etc., it will also cause the drill pipe to break

In summary, drill pipe failure is the result of the interaction of multiple factors. The main influencing factors should be refined and corresponding measures should be taken according to the specific drilling situation.


Measures to avoid abnormal failure of drill pipe

In order to avoid abnormal failure of drill pipe, we can start from improving the quality of drill pipe and standardizing operation.

Improving the quality of drill pipe:

Drill pipe material selection: Medium carbon alloy structural seamless steel pipe with high tensile strength, bending resistance and impact toughness should be selected. Commonly used materials are 36Mn2V, 35CrMo, 42MnMo7, 35CrMnSi, 45MnMoB, etc.

Joint structure improvement:

Stress dispersion groove: Designing a stress dispersion groove at the root of the drill pipe male joint can reduce stress concentration and improve bending resistance.

"Double top" structure: This structure tightens the inner shoulder and the end at the same time when the male and female buckles are tightened, which has better fatigue resistance.

Thread processing: Avoid incomplete threads at the thread terminals to prevent stress concentration and fatigue damage.

Construction process improvement:

Standard operation: Use the drill rod strictly in accordance with the allowable tension, torque and curvature radius of the drill rod to avoid overload.

Use appropriate thread sealing grease: Ensure the correct use and application of sealing grease to ensure the sealing and lubrication of threaded connections.


Through the above measures, abnormal failures of drill rods can be effectively reduced, the service life of drill rods can be increased, and economic losses can be reduced.

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