Material Selection for Oil and Gas Wells in O2-CO2 Coexistence Environment in Western China

Abstract With the popularization and application of production enhancement measures such as nitrogen gas injection gas lift and nitrogen drainage in oil and gas wells in western China, corrosion failures of wellhead devices, downhole tubing strings and tools occur frequently. Oxygen ingress has become one of the main causative factors inducing the failure of metallic materials. In this work, the corrosion behavior of a variety of materials in O2-CO2 coexistence environment was investigated. Based on the experimental results of general corrosion, maximum pitting rate, morphology and composition of corrosion products, the corrosion characteristics and possible mechanisms were discussed. The results showed that the presence of oxygen significantly enhanced the corrosion of low alloy steels (P110 and 3Cr) and stainless steels (13Cr and 316), especially promoted the localized corrosion of 13Cr stainless steel. The critical oxygen content and the suitability of several materials for use in oxygen-containing environments were discussed. Based on a comprehensive consideration of material upgrading, oxygen content control and the use of corrosion inhibitors, it was concluded that the combined use of low alloy steel and corrosion inhibitors may be a relatively more practical and economical solution.