Deposition and shear stress initial investigations for hydrate blockage

Over the past decade, the paradigm of gas hydrate research has transitioned from avoidance via thermodynamic inhibition toward management, where a limited amount of hydrate may be allowed to form in the flowline. This new paradigm enables new field development concepts, including longer-distance subsea tie-backs and limited chemical inhibition. This presentation reviews research datasets from flowloops on hydrate deposition phenomena and includes an initial analysis on the impact of shear stresses on hydrate deposits. This study integrates experimental data from unique high-pressure laboratory flowloops, including single-pass, gas-dominant and recirculating, liquid-phase flowloops. The flowloops have visual observation ports that allow video imaging to be performed throughout the high pressure tests. These apparatuses together are estimated to provide coverage over 1-200 Pa of flowing shear stress at the wall, over a range of total liquid inventories and water holdup. For this work, conceptual diagrams of deposition in oil, water, and gas-dominant systems are presented. Film growth rates are derived at the Colorado School of Mines (CSM) from visual observation in a deposition loop. Hydrate particle deposition rates are determined from a gas-dominant flowloop in Western Australia by fitting experimental data obtained from gas-dominant systems. The results demonstrate that the absolute shear stress required to prevent hydrate particles from depositing at the wall, or to remove/slough deposited hydrate from the wall, can vary with the primary fluid phase. Initial shear stress calculations from a specific test estimate that less than 5 Pa can be required to remove/slough hydrates from the wall in the aqueous phase, while more than 100 Pa may be required in a gas-continuous pipeline. This review suggests that deposition and flowing shear stress may be critical considerations in the design and operation of hydrocarbon systems, to help prevent hydrate blockage in industrial operations.