Morphology and Interphase Boundary Behavior of Gas Hydrates of Single, Binary, and Ternary Guests

Gas hydrates are a significant concern in flow assurance in oil and gas pipelines, because they can form plugs that translate into undesired costs and process safety risks. One key step in this process is the adherence of clathrates to the walls of the pipeline; therefore, understanding the surface behavior of gas hydrates is important. We present observations on the morphology and phase boundary behavior of hydrates of single (CH4, CO2, and C3H8), binary (CH4 + CO2 and CH4 + C3H8), and ternary (CH4 + CO2 + C3H8 and CH4 + C2H6 + C3H8) guests. At low growth rates, hydrates from single, binary, and ternary guests exhibited very similar morphologies. The contrary was true at higher velocities. Clathrate growth always proceeded via partial dissociation of the hydrate phase, regardless of guest composition or driving force. Propagation outside of the water boundary (halo) was found to be strongly dependent upon the composition of the gas phase, and mixtures with a high CO2 content produced the most halo. When part of the hydrate film was dissociated using a temperature gradient, these CO2 mixtures and the CH4 + C3H8 mixture exhibited migration of the liquid water toward the colder end of the sample slide. This water migration occurred simultaneously with halo growth at the opposite end of the slide. Halos stopped spreading over the substrate once the liquid water was depleted. This suggests that the halo growth mechanism is predominantly sustained by liquid water moving by capillarity between the substrate and the hydrate film.

Automated summary

Gas hydrates are a major concern in oil and gas pipelines as they can cause blockages and pose safety risks. Understanding the surface behavior of gas hydrates is crucial in flow assurance. The study presents observations on the morphology and phase boundary behavior of hydrates formed by different gas compositions. It was found that the growth and propagation of hydrates were influenced by the gas composition and driving force, with liquid water playing a significant role in halo growth.