Unveiling the Role of Hydrate Shedding in Subsea Gas Transportation: Accounting for Time-Varying Shear Strength

Under conditions of low temperature and high pressure, solid hydrates form inside submarine natural gas pipelines, continuously depositing on pipe walls, and eventually causing plugging. The deposited hydrates could shed off if their shear strength cannot withstand the shear force of airflow, significantly altering hydrate plugging process. Hydrate shear strength is determined by interparticle cohesion and would gradually increase with time, which has been universally ignored in current hydrate plugging modeling, leading to a failure in predicting plugging degree and status. In this study, we extended the classical Mohr–Coulomb criterion by introducing a time-dependent cohesion for hydrate particles and established a new relationship between the cohesion and shear strength for hydrate. When applying this relationship to hydrate plugging modeling of two well-measured experiments, the simulated results effectively capture the observed ascending-temporal trend of peak pressure drops during hydrate plugging process, accordingly becoming more aligned with experimental measurements. This demonstrates that the consideration of the increased shear strength with time is the critical importance of predicting ultimate plugging severity. Comparatively, the initial strength of hydrate deposition layer mainly affects the occurrence time of hydrate shedding events and the magnitude of peak pressure drop. A 10 Pa increase in initial hydrate shear strength could prolong the occurrence time for the shedding event by 4–9%, and enhance the peak pressure drop by 8–15%. According to the influence characteristics of hydrate shear strength, important insights and practical recommendations are also provided to proactively delay and mitigate hydrate plugging that occurs during subsea gas transport.