Trouble at the Bottom of the Ocean
Building on lessons learned from the failure of the first containment dome on Saturday, BP is currently considering two options to contain the ever-expanding oil spill in the Gulf of Mexico. One possibility is to lower a smaller dome, dubbed the "top hat," over the main leak. The other is to insert a tube directly into the leaking drill pipe to pump the oil and gas to the surface before it can be released into the water.
Both options are designed to avoid the formation of methane hydrate, a solid composed of methane (natural gas) and water that clogged the first containment system. (It's believed that methane gas triggered the explosion that caused the spill.) Produced when water molecules form a cage around methane molecules in relatively low temperature and under high pressure (such as deep under the sea), methane hydrate looks much like ice but readily bursts into flame when ignited. The smaller dome will hold a lot less water for the emerging methane to be exposed to and, additionally, will use heat and antifreeze to minimize hydrate formation. The riser-insertion tube, on the other hand, is intended to allow oil and gas to be pumped directly out of the leaking pipe before it can be exposed to any water, preventing hydrate formation entirely.
This isn't the first time methane hydrate has posed problems for the oil and gas industry. Hydrates became the focus of scientific study in the 1940s, when industry scientists discovered that methane hydrate was clogging up pipelines. Since then, the industry has developed a whole new field of study known as flow assurance. Using methanol as an antifreeze to prevent hydrate formation is the "heavy-hammer," tried-and-true approach to combating gas hydrates, says Timothy Collett, a research geologist at the U.S. Geological Survey, and it's that substance that BP will inject into the smaller containment dome. Scientists have also been studying other techniques for fighting hydrates, such as using newly developed polymers to prevent hydrates from sticking together and forming a plug.
Early research on how to avoid hydrate buildup eventually led to the discovery of naturally occurring methane hydrates in the '70s, which are found pretty much everywhere temperature and pressure conditions permit—in the sea-floor sediments of all oceans deeper than about 2,000 feet and in permafrost. The majority of the world's methane is stored in hydrate form rather than gas form.
These hydrates may have a number of practical applications. Gas hydrates might be an energy resource, and scientists are studying ways to safely extract them from the earth for their methane content. Hydrates have also been produced in the lab to use for purification purposes—like water desalinization—since the compounds take up pure water and leave behind impurities. Hydrates might also be used to ship methane—the idea would be to produce hydrates from natural gas and then ship them in that solid form for greater safety and efficiency.
Nevertheless, hydrates pose some serious risks beyond the havoc they've wreaked on containment efforts of the current oil spill. Many experts fear that there could be an offshore-drilling accident if a well is bored through a methane-hydrate deposit. In this case, says Rice University marine geologist Gerald Dickens, the heat of drilling or of pumping hot oil up from the well could potentially lead to dissociation, or melting, of a hydrate deposit, collapsing the surrounding sediment and releasing methane gas, with dire consequences such as a spill or damage to the drilling rig.
Beyond just the oil industry, methane hydrates could potentially exacerbate global warming, given that huge amounts of methane (a greenhouse gas 20 times more potent than CO2) could be released if some or all of the world's hydrates melted. Some climate scientists fear that our already warming climate could trigger massive releases of methane from hydrate, speeding along climate change at an unprecedented rate. But there is little evidence to suggest something like this could happen anytime soon. "There's a lot of catastrophism in this area," says USGS research geophysicist Carolyn Ruppel. It takes a long time for temperature changes to reach the depth where hydrates are, so atmospheric temperatures on the time frame of hundreds of years probably don't have that much effect on patterns of hydrate dissociation. Furthermore, the latest science suggests that relatively little, if any, methane hydrate is currently degassing, amounting to at most 2 percent of global methane emissions, and much of that may not even be entering the atmosphere. Most of the degassing hydrate would be deep underwater, so the methane that's released can get dissolved in the water or chewed up by certain microbes before it reaches the surface.
In the meantime, methane hydrate continues to serve as a formidable obstacle in attempts to clean up the oil spill, a disaster that faces too many obstacles already.
