They have hardly any refining capacity to actually use those reserves.
There's no doubt though that they feel having nuclear weapons will be a deterrent after how close they came to having their government wiped out by Cheney et. al.
They are trying to build _a_ bomb at this point. They are no where near the point they can deter the US from meddling. One bomb, however, will deter those with no bombs.
They should know better than anyone what the state of their reserves are. It would be a pity for them to squander the wealth that comes from selling their oil without having created any lasting infrastructure.
Desperately needed in a country with the world's third-largest oil reserves.