Premelting-Induced Agglomeration of Hydrates: Theoretical Analysis and Modeling

Abstract

Resolving the long-standing problem of hydrate plugging in oil and gas pipelines has driven an intense quest for mechanisms behind the plug formation. However, existing theories of hydrate agglomeration have critical shortcomings, for example, they cannot describe nanometer-range capillary forces at hydrate surfaces that were recently observed by experiments. Here, we present a new model for hydrate agglomeration which includes premelting of hydrate surfaces. We treat the premelting layer on hydrate surfaces such as a thin liquid film on a substrate and propose a soft-sphere model of hydrate interactions. The new model describes the premelting-induced capillary force between a hydrate surface and a pipe wall or another hydrate. The calculated adhesive force between a hydrate sphere (R = 300 μm) and a solid surface varies from 0.3 mN on a hydrophilic surface (contact angle, θ = 0°) to 0.008 mN on a superhydrophobic surface (θ = 160°). The initial contact area is 4 orders of magnitude smaller than the cross-sectional area of the hydrate sphere and can expand with increasing contact time because of the consolidation of hydrate particles on the solid surface. Our model agrees with the available experimental results and can serve as a conceptual guidance for developing a chemical-free environmentally friendly method for prevention of hydrate plugs via surface coating of pipe surfaces.

Clathrate Adhesion Induced by Quasi-Liquid Layer

“…For all fields mentioned above, the adhesive force between clathrates and natural or technical surfaces plays a significant role. This force drives the adhesion of clathrate particles to pipe surfaces in oil and gas pipelines and leads to plugging. − Similar problems happen in the facilities for clathrate productions, e.g., for storage of fuel gas. Synthetic clathrates tend to attach to equipment walls, accumulate, and finally block the reactors and circulation systems.…”

“…Residual water present in crude oil or natural gas tends to form clathrate particles which then accumulate at the pipe surfaces and plug the flow. 26 − 28 …”

“…High storage capacity and slow liberation of gas upon dissociation enable efficient and safe storage of fuel gas based on clathrates. , Nevertheless, clathrates are a major safety hazard in the oil and gas industry. Residual water present in crude oil or natural gas tends to form clathrate particles which then accumulate at the pipe surfaces and plug the flow. − …”

“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

“…Clathrates are considered as the next-generation material for fuel gas storage. − They are host–guest inclusion structures in which water molecules coordinate via hydrogen bonding (H-bonding) to form a cage-like framework that serves as a host structure . “Guest” molecules with suitable sizes are incorporated into the regular cavities of the host structure. , In this way, the largest part of methane on Earth is encapsulated in natural clathrates, commonly named as combustible ice, − which constitute a vast untapped source of low-carbon energy that is far cleaner than oil and coal. ,,− Meanwhile, synthetic clathrates offer a rare opportunity for technical fuel gas storage . Fuel gas such as methane and hydrogen can be encapsulated in the cavities of clathrate structures at mole fractions in the order of 0.1.…”

Assessment of Hydrate Formation, Storage Capacity, and Transport Properties of Methane and Carbon Dioxide through Functionalized Carbon Nanotube Membranes

“…Reversible hydrate formation technology is an effective approach for the desalination of saline water , and gas separation. − Hydrate formation can also be considered as a secure and lasting approach for CO 2 sequestration when CO 2 is injected into geological formations. , Since gas hydrates have a significant impact on industries, they have received considerable attention over the past few decades.…”