Research and Application of Anti-corrosion Technology for Tungsten Alloy Coated oil Pipes

The downhole environment of acid gas reservoirs typically contains both H₂S and CO₂, often accompanied by water, which creates extremely harsh corrosion conditions and presents significant challenges for long-term safe production. Currently, the anti-corrosion measures employed in sulfur-containing gas wells primarily include the use of corrosion inhibitors and material-based solutions. However, corrosion inhibitors are only effective for protecting the tubing above the injection valve and do not provide adequate protection for lower tubing sections, revealing notable technological limitations. On the other hand, while nickel-based alloy materials exhibit excellent corrosion resistance, their high cost poses a barrier to economic viability. In response to these challenges, this paper introduces a novel completion anti-corrosion technology—tungsten alloy coated tubing anti-corrosion technology. This approach offers superior corrosion resistance along with a relatively low-cost advantage and has been widely implemented in both domestic and international oilfields. Nevertheless, its adaptability within medium to high sulfur gas reservoirs requires further investigation. To address this gap, we systematically conducted evaluation experiments focusing on various aspects including physical and chemical properties, mechanical properties, corrosion resistance, erosion resistance, and thread sealing performance of tungsten alloy coated tubing. The experimental results indicate that under five typical working conditions—including those found in the high-grind Dengying Formation as well as high-sulfur gas reservoirs in northeastern Sichuan and shale gas—the corrosion rate of tungsten alloy coated tubing remains below 0.05 mm/a; thus categorizing it as mild corrosion. Furthermore, during make-up and break-out tests (comprising 10 make-ups and 9 break-outs), no instances of sticking or noticeable damage were observed. Additionally, the coated threads successfully passed API RP 5C5 standard CAL IV level evaluation tests; importantly, thread gas sealing performance remained unaffected under extreme tensile, compressive, and bending loads—thereby meeting all design requirements associated with triaxial applications.