As the world’s appetite for oil and gas continues to increase while access to easily accessible reserves decreases, deep-sea oil and gas wells are being positioned in ever-deeper waters. The dangers and difficulties faced in such operations were highlighted in 2010 with the Deepwater Horizon oil spill. While placing a containment dome over a leak and piping the oil to a surface storage vessel had worked on leaks in shallower water, the attempt to do the same on the Deepwater Horizon’s largest leak failed when the formation of methane hydrate crystals blocked the opening at the top of the dome. Now researchers at MIT have developed surface coatings that can inhibit the buildup of these methane hydrates and keep the gas and oil flowing.
Methane hydrate is a solid cage-like compound – or clathrate – that forms under very high pressure in which a large amount of methane is trapped within a crystal structure of water to form an ice-like solid. Although it was originally thought to only occur in the outer reaches of the solar system, it is now estimated that total amount of methane contained in hydrates in the world’s seafloor is much greater than the total known reserves of all other fossil fuels combined.
Much like the buildup of grease on the inside of a kitchen drain or sewer, the buildup of methane hydrates - which can form when methane comes into contact with cold water in the depths of the ocean - inside a well casing or on the inner walls of pipes that carry oil or gas from the ocean depths can restrict or even block the flow of gas or oil. It was this kind of blocking that caused the failure of the containment dome technique attempt on the Deepwater Horizon leak.
Current techniques to prevent this happening include the heating or insulation of the pipes – which is expensive - or adding methanol into the flow of gas or oil – which can harm the environment if it escapes.
An MIT team led by associate professor of mechanical engineering Kripa Varanasi had been looking for a solution to this problem even before the Deepwater Horizon spill and now say they have found it. Having already studied the use of superhydrophobic surfaces to prevent the buildup of ordinary ice on things such as aircraft wings, the team decided to examine whether similar surfaces could be used to keep pipe walls clear of methane hydrates.
Using a simple “hydrate-phobic” coating, Varanasi and his colleagues were able to reduce the adhesion of hydrates in a pipe to one-quarter the amount compared to untreated surfaces.
“The oil and gas industries currently spend at least $200 million a year just on chemicals” to prevent methane hydrate buildups, Varanasi says. However, the total figure for prevention and lost production due to hydrates would be much, much higher. Using passive coatings on the insides of pipes would be much cheaper than current prevention techniques and allow the use of containment domes to capture flows from leaks in much deeper waters than is currently possible.
Additionally, the team says the test system they devised provides a simple and inexpensive way to search for even more effective inhibitors. They say their findings are also applicable to other adhesive solids, such as solder adhering to a circuit board, or calcite deposits inside plumbing lines. The testing methods developed by the researchers could also be used to evaluate coatings for a variety of commercial and industrial processes.
The team’s findings are detailed in a paper published in the journal Physical Chemistry Chemical Physics.