New method avoid methane hydrates buildup undersea

New method to avoid methane hydrates buildup undersea

6:29 AM, 16th April 2012
New method to avoid methane hydrates buildup undersea
A block of a gas hydrate (methane clathrate) recovered from seafloor sediments off the Oregon coast. Photo: Wusel007/Wikipedia.

CAMBRIDGE, US: Methane hydrates, which can freeze upon contact with cold water in the deep ocean, are a chronic problem for deep-sea oil and gas wells. 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. Researchers at MIT, led by Kripa Varanasi, Associate Professor, MIT have found a solution for this.

According to Varanasi, the deep sea is becoming ‘a key source’ of new oil and gas wells, as the world’s energy demands continue to increase rapidly. But one of the crucial issues in making these 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. The 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. “Although they look like ordinary ice, methane hydrates form only under very high pressure, in deep waters or beneath the seafloor,” said J David Smith, Graduate Student, MIT. By some estimates, the total amount of methane contained in the world’s seafloor clathrates greatly exceeds the total known reserves of all other fossil fuels combined.

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.

The 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 what he calls ‘hydrate-phobic’ surfaces to prevent hydrates from adhering tightly to pipe walls. Because methane hydrates themselves are dangerous, the researchers worked mostly with a model clathrate hydrate system that exhibits similar properties.

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.

© MIT News

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