I don't pretend to know the state of the books for OPEC's countries, but I imagine they have a significant chunk of change set aside, and won't find that prolonged low prices won't be a particular impediment.
The extraction techniques for both Alberta's Tar Sands, and the Shale fields in the US are much more expensive to run. Back in August of this past year, the rumblings of "cutting costs" were already starting to roll around the oil patch in Calgary.
I predict that the downturn we will experience in Alberta will be at least as severe, if not more so, than we saw in 1980. If prices stay low for more than a couple of months, the oil patch will start axing investment and people at a ferocious rate. We're just coming through to the end of the first full quarter of these low prices, and probably around the end of the next quarter we will start to see things happen as companies start to try to keep themselves profitable.
There are already modest scale layoffs happening in downtown Calgary, and larger cuts are yet to come. Companies like Talisman Energy have bought themselves a bit of time by selling off to new ownership - it will take a few months for the new owners to start intervening. But other companies are already making major changes to their capital investment plans, with cuts being announced almost daily. If you don't think this is going to be a messy time in Alberta, just wait and watch - it's not going to be pretty.