That would be bad for a oil refinery as different crude oil sources have different contents. Some refinery must corrosion resistant metals or the crude will corrode them quickly, others can use cheap iron pipes.

This assumes the refinery isn't in on the fraud. If they are in on it they know what they are getting and there won't be a problem.

Of course I don't know the grades of oil from either place. (if I did know enough I'd probably not be allowed to talk about it...) It could be this substitution is fine for the refineries.