Hydrate Formation And Growth In Pipeline Research Paper

2.12 Hydrate Formation and Growth in Pipeline.

As discussed above, Hydrate formation begins when fluid temperature drops below a certain level and starts to nucleate close to the hydrocarbon phase on a water droplet in gas, oil or condensate phases. Hydrates grow along the surface of a droplet, until it is completely covered with a thin hydrate layer. Then, water will penetrates from the interior of the water droplet to the surface of the hydrophilic hydrate surface next to the hydrocarbon phase through micro-perforations or small cracks in the hydrate film as shown in Figure 2.14. The thickness of hydrate layer formed depends on the hydrate formation driving force and shear forces on the droplets. Hydrate formation rate will decreases as the thickness

Sub-cooled water inside the droplet will drain through these cracks and spread on the dry hydrophilic hydrate film. Hydrate-forming species close to the pipe wall may convert this water to hydrate quickly, often resulting in deposition of the hydrate/water droplet on the wall.

In turbulent liquid systems the water phase is often distributed in the hydrocarbon phase as rough, unstable water-in-oil emulsions. As surface tension of the droplets increases due to the hydrate layer, the water droplets agglomerate to larger droplets or water lumps in order to minimise surface area, as shown in figure 2.15.

In turbulent liquids these water lumps will change form, surface area and volume continuously. The thin hydrate layer on the water lump will therefore often be broken, giving new water-hydrocarbon interfaces where more hydrates quickly form. The turbulent forces will also create small hydrate covered water droplets as shown in figure 2.16. Due to the hydrophilic properties of the hydrate surface, these droplets will be absorbed in the water lumps giving a slush-like appearance (Aalvik