So right now, they're flaring off natural gas in North Dakota from the Bakken oil fields because it's not worth their time, money, or effort to take it to market. Figure out how to transport that to someplace they need it, or to build something that can take advantage of cheap gas there. (http://www.nytimes.com/2011/09/27/business/energy-environmen...)

If you're going to use a ship for this, it would also have to be able to liquefy the natural gas (you have can store about 1000 times more energy with natural gas as a liquid than as a gas)

Basically, the capital costs and operating costs for this probably don't make any economic sense.