Technical status and prospect of high-strength low-alloy-steel OCTG for deep high-sulfur gas wells

China is rich in deep high-sulfur oil and gas resources with great potential, which are the important replacement resources in the future. However, the exploration and development and harsh working conditions (ultra-high temperature, ultra-high pressure, and high sour gas content) of deep oil and gas exert higher challenges and requirements on the strength and sulfide stress cracking (SSC) resistance of oil well string. The lightweight and integrity of oil well string are the important guarantee for its safe and efficient development, which puts forward higher requirements for strength and SSC resistance of oil country tubular goods (OCTG). The increasing of strength can increase the SSC susceptibility, so the matching between strength-toughness and SSC resistance is the key to the safe service of OCTG. After analyzing the SSC mechanisms and influencing factors of steel OCTG, this paper investigates the technical status of the product system, material development and SSC test evaluation of high-strength low-alloy steel sulfur-resistant OCTG, and predicts the future development direction. The following results are obtained. First, the essence of SSC in steel OCTG lies in the interaction between hydrogen and defects in steels, while metallurgical factors (such as chemical elements, and microstructure) control the type, quantity and distribution of defects in steels. Second, obtaining uniform and fine martensitic structure and uniformly dispersed nanoscale carbides by means of chemical composition optimization, nanoscale precipitation phase control, inclusion optimization, and dislocation density reduction is an effective way to improve the SSC resistance of 125 ksi steel. Third, the traditional SSC test methods are no longer applicable to the evaluation of high-strength sulfur-resistant OCTG, so it is necessary to establish the SSC risk classification indexes suitable for deep wells, and the full-scale SSC evaluation method applicable to the high-strength sulfur-resistant OCTG used for ultra-deep wells. In conclusion, it is proposed to make use of the material gene engineering technology to speed up the composition-structure design and development concept of sulfur-resistant OCTG with theoretical significance and application value. What's more, it is necessary to continue to accelerate the research and development of 125 ksi sulfur-resistant OCTG, and determine its quality control system and application boundaries, so as to support the safe service of high-strength sulfur-resistant OCTG for deep high-sulfur gas wells. © 2024 Natural Gas Industry Journal Agency. All rights reserved.