Multiple controlling factors for methane hydrate formation in water-continuous system

Abstract

Hydrate formation in a water-continuous system is a serious production and safety issue when developing oil, gas, and natural gas hydrate in deep water. In this work, several controlling factors, such as bubble breakage, coalescence, deformation, bubble-eddy collision, and bubble-bubble collision, are introduced, as we believe these must be considered when researchers study hydrate formation in a water-continuous system. A mass transfer model including the controlling factors under discussion is developed based on hydrate formation experiments, which are conducted under void fractions of 3.0% and 4.5% and flow velocities from 0.95 m/s to 1.40 m/s. Bubble breakage and deformation increase the interfacial area during hydrate formation in bubbly flow. Bubble deformation induces an increase in the interfacial area of approximately 10%, and is a more dominating controlling factor than bubble breakage or coalescence. Bubble-eddy collision and the bubble-bubble collision greatly improve the overall mass transfer coefficient between gas and liquid, and enhance hydrate formation in bubbly flow. In the low flow velocity condition, the model that considered bubble breakage, coalescence, and deformation predicted the hydrate formation rate in bubbly flow accurately with an absolute error below 6%. However, in the high flow velocity condition, although the absolute error of the original model dropped from 30% to 21% when bubble breakage, coalescence, and deformation were taken into account, the additional inclusion of the universal factor resulted in a decrease in absolute error to 3.5%. Considering the controlling factors discussed in this work could significantly improve the accuracy of the hydrate formation model, and bring it closer to industrial conditions.