Views: 222 Author: Rebecca Publish Time: 2024-12-24 Origin: Site
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>> Corrosion
>> Human Error
● Factors Influencing Coiled Tubing Failures
● Preventive Measures and Maintenance
● Case Studies of Coiled Tubing Failures
● Frequently Asked Questions (FAQ)
>> 1. What are the main causes of coiled tubing failure?
>> 2. How does corrosion affect coiled tubing?
>> 3. What preventive measures can be taken against coiled tubing failures?
>> 4. At what depths do most coiled tubing failures occur?
>> 5. How can operators monitor coiled tubing integrity?
Coiled tubing (CT) is an essential technology in the oil and gas industry, utilized for various applications such as well intervention, drilling, and workover operations. Despite its advantages, coiled tubing can experience failures due to several factors, including mechanical damage, corrosion, and fatigue. Understanding these failure modes is crucial for improving operational safety and efficiency.
Coiled tubing is a continuous length of steel pipe that is wound onto large reels. It can be deployed into wells for various tasks without the need for traditional drill pipes. The coiled tubing's flexibility allows it to navigate complex wellbore geometries, making it suitable for a range of operations, including:
- Well cleanouts
- Acid stimulation
- Fracturing
- Cementing
- Logging
- Plug setting or retrieval
The tubing typically varies in diameter from 1 to 3.5 inches and can be several thousand feet long. Its ultimate tensile strength ranges from 80,000 to 140,000 psi, which is critical for withstanding the pressures encountered during operations.
Coiled tubing failures can occur due to various reasons, which can be broadly categorized into mechanical damage, corrosion, and human error.
Mechanical damage is often caused by:
- Fatigue: Repeated bending and straightening during deployment lead to micro-cracks that can propagate over time. This phenomenon is known as ultralow cycle fatigue.
- Buckling: This occurs when the tubing encounters obstructions or changes in borehole diameter, leading to deformation and potential failure.
- Weld-related Issues: The welds in coiled tubing can be points of weakness due to stress concentration and microstructural anomalies.
Corrosion is a significant contributor to coiled tubing failures. It can manifest in several forms:
- Localized Corrosion: This type of corrosion results in isolated wall loss within the tubing string. It is often exacerbated by the presence of corrosive fluids such as brine or H2S (hydrogen sulfide).
- Microbiologically Influenced Corrosion (MIC): Anaerobic bacteria can form biofilms on the steel surface, leading to pitting and accelerated degradation.
- General Corrosion: Uniform mass-loss corrosion can occur over time due to exposure to corrosive environments.
Corrosion-related failures account for approximately 30% of premature retirements in coiled tubing strings.
Human error can also play a role in coiled tubing failures. Mistakes during deployment or operation—such as exceeding tensile load limits—can lead to catastrophic failures. Operators must adhere strictly to safety protocols and guidelines to mitigate these risks.
Several factors influence the likelihood of coiled tubing failures:
- Operating Environment: Highly corrosive environments increase the risk of corrosion-related failures. For example, H2S environments contribute significantly to failure rates.
- Well Depth: Most failures occur at depths between 5,001 and 10,000 feet. The increased axial loads at greater depths heighten the risk of both fatigue and tensile overload failures.
- Material Grade: Coiled tubing comes in various grades (70, 80, and 100), with higher-grade materials generally exhibiting better resistance to failure under similar conditions.
To minimize the risk of coiled tubing failures, operators must implement effective preventive maintenance strategies:
- Regular Inspections: Continuous monitoring of tubing integrity using technologies like CoilScan helps identify anomalies before they lead to failures.
- Corrosion Mitigation: Employing corrosion inhibitors and ensuring proper fluid management during operations can significantly reduce corrosion rates.
- Fatigue Management: Keeping precise records of cycle life and retiring tubing strings after reaching their fatigue limits are critical practices that help extend service life.
Several case studies illustrate the consequences of coiled tubing failures:
1. Case Study A: A coiled tubing string failed due to excessive fatigue after being deployed in a high-pressure environment without adequate monitoring of its cycle life.
2. Case Study B: Corrosion-induced pitting led to a catastrophic failure during a workover operation in an H2S-rich environment. The failure resulted in significant downtime and financial losses for the operator.
3. Case Study C: Mechanical buckling occurred when the coiled tubing encountered an obstruction at depth, leading to a complete loss of pressure integrity.
Understanding what happens when coiled tubing fails is crucial for operators in the oil and gas industry. By recognizing common failure modes such as mechanical damage, corrosion, and human error—and implementing preventive maintenance strategies—operators can significantly reduce the risk of catastrophic failures. Continuous monitoring and adherence to safety protocols are essential for maintaining the integrity of coiled tubing systems.
The primary causes include mechanical damage (fatigue and buckling), corrosion (localized and microbiologically influenced), and human error during operations.
Corrosion leads to wall thinning and pitting, which can significantly weaken the structure of the tubing and increase the likelihood of failure.
Regular inspections, corrosion mitigation strategies, and careful management of fatigue cycles are essential preventive measures.
Most failures occur between depths of 5,001 and 10,000 feet due to increased axial loads at greater depths.
Operators can use advanced inspection technologies like CoilScan for continuous monitoring of wall thickness and other integrity metrics throughout operations.
[1] https://www.ogj.com/home/article/17215849/pitting-tensile-overloading-produce-most-coiled-tubing-failures
[2] https://www.piprocessinstrumentation.com/maintenance-safety/article/15563762/coiled-tubing-preventive-maintenance-and-corrosion-failure-mitigation
[3] https://petrowiki.spe.org/Coiled_tubing_fatigue
[4] https://hrcak.srce.hr/file/404438
[5] https://www.slb.com/videos/coiled-tubing-inspection-technology-and-operation
[6] https://www.bsee.gov/sites/bsee.gov/files/tap-technical-assessment-program/300aq.pdf
[7] https://drillingforgas.com/en/production/coiled-tubing-operations-and-hse-considerations
[8] https://www.researchgate.net/publication/314741866_An_Analysis_of_Failures_in_Coiled_Tubing
[9] https://oilandgasoverview.com/coiled-tubing-fatigue-getting-more-life-from-coiled-tubing-string/
[10] https://www.researchgate.net/figure/Fracture-surfaces-of-four-of-the-tested-coiled-tubing_fig10_277680601
[11] https://www.tenaris.com/en/news/2021/tenaris-presents-research-on-coiled-tubing-failures-during-spe-icota
[12] https://www.petrosync.com/blog/what-is-coiled-tubing/
