I think you jave it backwards. The US committed all refineries to heavy crude oil shortly before it discovered how to frack for the high grade stuff. But because it would have cost oil companies hundreds of billions to convert all the refineries they just got done making, we import shitty tar sand oil from Canada and export all the high grade stuff we drill for.

But yeah, Venezuela's heavy crude is what ExxonMobile wants to bring into Houston so that my boss's new truck can continue to get 16 MPG on the highway.