Full-aluminum alloy drill pipes with both pipe body and tool joints made of aluminum alloy can reduce the risks associated with cementing operations in oil and gas wells. However, no detailed failure analysis reports on their field applications have been published to date. Following the initial application of a 7075 series full-aluminum alloy drill pipe in an ultra-deep section of well SDCK1 during cementing operations, severe corrosion was observed on the pipe body, and fracture occurred in the joint during subsequent breakout operations. This paper presents a failure analysis of the full-aluminum alloy drill pipe under high-temperature oil-based drilling fluid conditions. The analysis employed chemical composition analysis, scanning electron microscopy (SEM), metallographic examination, x-ray diffraction (XRD) analysis, mechanical property testing, and energy-dispersive x-ray spectroscopy (EDS). The research indicates that the yield strength of the aluminum alloy tends to decrease with increasing temperature, with a more rapid decline observed when the temperature exceeds 80 °C. Furthermore, the yield strength of the aluminum alloy material in the drilling fluid environment is significantly lower compared to that in an air environment. Additionally, the hardness of both the failed aluminum alloy drill pipe body and the joint was significantly reduced. Corrosion is identified as the primary cause of failure in the aluminum alloy pipe body. The corrosion products mainly consist of powdery deposits and fibrous structures, both composed of AlO(OH) and Al2O3. The fibrous corrosion products are more detrimental to the aluminum alloy matrix than the powdery ones. Stress corrosion fatigue is the main failure mechanism for the aluminum alloy joint. The high-temperature downhole environment further accelerated the corrosion process and the reduction in matrix strength, while torsional stresses from makeup/breakout operations and tensile stresses accelerated the fracture process of the aluminum alloy joint. To prevent failure accidents involving full-aluminum alloy drill pipes, optimization measures are proposed from three aspects: enhancing the high-temperature resistance of the aluminum alloy material, refining its microstructure, and reducing the corrosion rate of the aluminum alloy drill pipe. The research results can provide a theoretical and practical basis for the application and optimization of full-aluminum alloy drill pipes.

Failure Analysis of Full-Aluminum Alloy Drill Pipe under High-Temperature Oil-Based Drilling Fluid Conditions

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发表日期：

2026年7月23日

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Cai Mingjie

摘要

Full-aluminum alloy drill pipes with both pipe body and tool joints made of aluminum alloy can reduce the risks associated with cementing operations in oil and gas wells. However, no detailed failure analysis reports on their field applications have been published to date. Following the initial application of a 7075 series full-aluminum alloy drill pipe in an ultra-deep section of well SDCK1 during cementing operations, severe corrosion was observed on the pipe body, and fracture occurred in the joint during subsequent breakout operations. This paper presents a failure analysis of the full-aluminum alloy drill pipe under high-temperature oil-based drilling fluid conditions. The analysis employed chemical composition analysis, scanning electron microscopy (SEM), metallographic examination, x-ray diffraction (XRD) analysis, mechanical property testing, and energy-dispersive x-ray spectroscopy (EDS). The research indicates that the yield strength of the aluminum alloy tends to decrease with increasing temperature, with a more rapid decline observed when the temperature exceeds 80 °C. Furthermore, the yield strength of the aluminum alloy material in the drilling fluid environment is significantly lower compared to that in an air environment. Additionally, the hardness of both the failed aluminum alloy drill pipe body and the joint was significantly reduced. Corrosion is identified as the primary cause of failure in the aluminum alloy pipe body. The corrosion products mainly consist of powdery deposits and fibrous structures, both composed of AlO(OH) and Al₂O₃. The fibrous corrosion products are more detrimental to the aluminum alloy matrix than the powdery ones. Stress corrosion fatigue is the main failure mechanism for the aluminum alloy joint. The high-temperature downhole environment further accelerated the corrosion process and the reduction in matrix strength, while torsional stresses from makeup/breakout operations and tensile stresses accelerated the fracture process of the aluminum alloy joint. To prevent failure accidents involving full-aluminum alloy drill pipes, optimization measures are proposed from three aspects: enhancing the high-temperature resistance of the aluminum alloy material, refining its microstructure, and reducing the corrosion rate of the aluminum alloy drill pipe. The research results can provide a theoretical and practical basis for the application and optimization of full-aluminum alloy drill pipes.