Decomposition Characteristics of Hydrate Sediment Shedding Blocks under Flow Conditions: Effect of Temperature, Inhibitor Concentration, and Stirring.

The dynamics of the hydrate deposit layer and its potential risks during the flow assurance process of oil and gas transmission pipelines have not been fully clarified. Although existing measures can affect the sedimentary layer, the dislodged blocks generated during its decomposition may trigger secondary plugging, which in turn threatens the safe operation of pipelines. In this study, the decomposition pattern of the hydrate shedding block was investigated by a visual high-pressure reactor at different temperatures (3-11 °C), stirring rates (0-200 rpm), and methyl ethylene glycol (MEG) concentrations (0-40 wt %), with hydrate formation at 5 MPa and decomposition at 1.013 MPa. The study has, for the first time, discovered that a critical temperature exists in the decomposition process. When temperatures fall below this critical threshold, decomposition is governed by heat transfer or diffusion; upon reaching or exceeding this value, the process shifts to being dominated by interfacial reactions, resulting in a "sensitive jump" in decomposition rate. Further research reveals that the promoting effect of fluid shear (stirring) exhibits temperature dependency: at a low temperature of 3 °C, vigorous stirring at 200 rpm can increase the decomposition rate by over 330%; however, at temperatures ≥9 °C, this enhancing effect significantly diminishes. Additionally, a nonlinear synergistic relationship exists between MEG concentration and stirring intensity: moderate MEG concentrations (10-20%) exhibit optimal synergistic effects with 150 rpm stirring, whereas excessive MEG (≥30%) actually diminishes the stirring enhancement effect. It is suggested for the first time that there may be sensitive jump values or intervals for hydrate decomposition, and an operational window for the synergistic regulation of "inhibitor concentration-fluid shear" is established, which provides a new kinetic regulation strategy for the safe development of hydrates.