Multi‑Medium Coupled Corrosion, Service‑Boundary Evolution and Integrity Management of Downhole Tubulars in High‑Sour Gas Fields: A Review

Downhole tubulars in high-sour gas fields operate under extremely harsh conditions rarely seen in other industrial scenarios. With H2S partial pressures exceeding 1 MPa, Cl- concentrations reaching 2×105 mg·L-1 and frequent elemental sulfur deposition, the synergistic action of these corrosive species drives corrosion rates and cracking susceptibilities far beyond predictions from conventional single-medium tests. Based on field experience from China’s major high-sour gas blocks and extensive published literature, this review maps the operating window onto a three-dimensional service-boundary space defined by H2S partial pressure, temperature and Cl- concentration, and illustrates how temperature-dependent reaction pathways of elemental sulfur significantly shrink the valid service window of tubular materials. It clarifies the chained-evolution law among mass-loss, localized-defect and environment-assisted cracking failures, revealing that abrupt tubular failures typically occur after material service boundaries are exceeded. Five typical tubular material systems are compared regarding cost, mechanical performance and corrosion resistance. Advances in corrosion inhibitors, surface coatings and localized monitoring are reviewed, a closed-loop integrity-management framework for life-extension decision-making is proposed, and key technical bottlenecks for super-deep wells and emerging scenarios including CCUS, geothermal exploitation and underground hydrogen storage are highlighted.