Cept, the gas really isn't going overseas. I don't know where people got that. Well, I do, I guess. But it's not true. Yet.
There have been lots of discussions about "shipping" large amounts. Currently, only 2 ports in the USA export gas, one in Louisiana and another in Alaska. If any Marcellus gas has been "shipped" thus far, it's fractions of a %. Because of the glut of gas supply in our pipeline system from Marcellus, there are now 20 some idle IMPORT ports. We no longer have the need to import much gas like we used to. These ports are hooked up to pipelines. There has been great discussion politically about reversing these import sites, and the pipelines which feed them, to make them export sites. i.e. ship out instead of in. President Obama is even in support. Many have applied for DEP permits to carry through on this, but thus far only a few have been approved and none have completed the switch and are capable of shipping shale gas. The sites do have to be physically reconfigured to export gas. But the price of that reconfiguration is certainly less than building a greenfield site.
I was trying to use the term "shipping" instead of export. Because the vast majority of shale gas, like traditional gas, is currently a pipeline game. Each well connects to a pipeline. The gas each well puts in is metered. The gas each user takes out is metered. But it is not traced where each molecule comes from. These pipelines do NOT go overseas, but the grid is indeed one and the same as Canada's grid. So technically, yes, a fair % is "exported" over the Canadian border, and to a lesser extent, the Mexican border. But so far 99+% of it is being used in North America and not "overseas."