Impact of hydrogen blending on flow assurance assessment in subsea natural gas pipelines

Hydrogen blending into offshore natural gas pipelines is increasingly regarded as a transitional decarbonization pathway; however, its implications for deep-water subsea flow assurance remain insufficiently understood. This study presents a field-validated assessment of hydrogen–natural gas co-transport in a deep-water subsea pipeline, integrating hydraulic, thermal, corrosion, erosion, hydrate, vapor-fraction, and heat-transfer analyses within a unified modeling framework. The Atoll gas field (Eastern Mediterranean, approximately 920 m water depth) is selected as a representative case study. A 20-inch subsea production and export pipeline system is simulated using Aspen HYSYS® Version 14 and validated against High Integrity Pipeline Protection System (HIPPS) field data, with deviations below 3 %. Hydrogen blending levels ranging from 0 to 50 vol% are investigated. The results indicate that hydrogen enrichment reduces overall pressure losses and enhances vapor-phase stability due to lower mixture density, while increasing flow velocity and erosion-related parameters within acceptable operational limits. Accelerated cooling associated with hydrogen’s higher thermal conductivity increases operational hydrate risk, governed primarily by thermo-hydraulic effects rather than hydrate thermodynamics. A 50 % hydrogen blend is adopted as a conservative upper-bound scenario to examine limiting flow assurance behavior. Overall, the findings provide practical insights for offshore hydrogen blending feasibility and preliminary flow assurance screening.