MIT researchers develop surface coatings to inhibit buildup of methane hydrates that can block deep-sea oil and gas pipelines
Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Researchers at MIT, led by associate professor of mechanical engineering Kripa Varanasi, say they have found a solution, described recently in the RSC journal Physical Chemistry Chemical Physics.
Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation.
...A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations.—
Methane hydrates can freeze upon contact with cold water in the deep ocean, are a chronic problem for deep-sea oil and gas wells. As just one extreme example, early efforts at fixing the ruptured Deepwater Horizon well in 2010 by using a containment dome were stymied because the dome almost instantly became clogged with frozen methane hydrate. Sometimes these frozen hydrates form inside the well casing, where they can restrict or even block the flow, at enormous cost to the well operators.
One of the crucial issues in making deep wells viable is “flow assurance”: finding ways to avoid the buildup of methane hydrates. Presently, this is done primarily through the use of expensive heating systems or chemical additives. The oil and gas industries currently spend at least $200 million a year just on chemicals to prevent such buildups, Varanasi says; industry sources say the total figure for prevention and lost production due to hydrates could be in the billions. The MIT team’s new method would instead use passive coatings on the insides of the pipes that are designed to prevent the hydrates from adhering.
These hydrates form a cage-like crystalline structure, called clathrate, in which molecules of methane are trapped in a lattice of water molecules. Inside the pipes that carry oil or gas from the depths, methane hydrates can attach to the inner walls and, in some cases, eventually block the flow entirely. Blockages can happen without warning, and in severe cases require the blocked section of pipe to be cut out and replaced, resulting in long shutdowns of production. Present prevention efforts include expensive heating or insulation of the pipes or additives such as methanol dumped into the flow of gas or oil. Methanol is a good inhibitor, Varanasi notes, but is very environmentally unfriendly if it escapes.
Varanasi’s research group has long focused on ways of preventing the buildup of ordinary ice—such as on airplane wings—and on the creation of superhydrophobic surfaces, which prevent water droplets from adhering to a surface. So Varanasi decided to explore the potential for creating “hydrate-phobic” surfaces to prevent hydrates from adhering tightly to pipe walls.
The study produced several significant results: First, by using a simple coating, Varanasi and his colleagues were able to reduce hydrate adhesion in the pipe to one-quarter of the amount on untreated surfaces. Second, the test system they devised provides a simple and inexpensive way of searching for even more effective inhibitors. Finally, the researchers also found a strong correlation between the “hydrate-phobic” properties of a surface and its wettability—a measure of how well liquid spreads on the surface.
The basic findings also apply to other adhesive solids, Varanasi says—for example, solder adhering to a circuit board, or calcite deposits inside plumbing lines—so the same testing methods could be used to screen coatings for a wide variety of commercial and industrial processes.
The research team included MIT postdoc Adam Meuler and undergraduate Harrison Bralower; professor of mechanical engineering Gareth McKinley; St. Laurent Professor of Chemical Engineering Robert Cohen; and Siva Subramanian and Rama Venkatesan, two researchers from Chevron Energy Technology Company. The work was funded by the MIT Energy Initiative-Chevron program and Varanasi’s Doherty Chair in Ocean Utilization.
J. David Smith, Adam J. Meuler, Harrison L. Bralower, Rama Venkatesan, Sivakumar Subramanian, Robert E. Cohen, Gareth H. McKinley and Kripa K. Varanasi (2012) Hydrate-phobic surfaces: fundamental studies in clathrate hydrate adhesion reduction. Phys. Chem. Chem. Phys., 14, 6013-6020 doi: XXX10.1039/C2CP40581DXX