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| Failure Causes and Countermeasures of Downhole Pipe String in a Gas Field |
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| DOI：10.7643/issn.1672-9242.2023.01.013 |
| KeyWord:downhole pipe string carbon steel gap corrosion thread grease coupling solutions |
| Author | Institution |
| LUO Yi |
CNOOC Tianjin Pipeline Engineering Technology Co., Ltd., Tianjin , China |
| XIA Ming-lei |
CNOOC Tianjin Pipeline Engineering Technology Co., Ltd., Tianjin , China |
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| Abstract: |
| The work aims to analyze the failure cause of downhole pipe string in a gas field, and put forward effective solutions to reduce the recurrence of similar accidents. Through macro analysis, tensile properties, chemical composition analysis, metallographic analysis, corrosion product analysis, water quality analysis and scaling prediction, the possible causes of downhole pipe string corrosion in a gas field were deeply analyzed. The tensile properties, chemical composition and metallographic microstructure of the failed parts met the standard requirements, and the corrosion caused by material defects was excluded. The macro analysis showed that there was a gap between the external thread of the oil pipe and the internal thread of the coupling and the boring, and the screw thread grease was not precoated at the gap, so the gap corrosion occurred in the corrosive environment containing a large amount of Cl‒. In addition, because the formation water was easy to scale, when CaCO3 scale and sand sample were deposited at the gap, the condition for gap corrosion was constituted again, accelerating the corrosion. It is necessary to precoat thread grease at the screw joint of coupling and oil pipe during operation of downhole pipe string to prevent gap corrosion caused by corrosive medium in service environment and avoid reducing the service life of downhole pipe string. |
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