In other words, What can the Saudis achieve other than an interruption of fracking?
It's called a price war. The Saudis want to push the price so low that it kills the fracking boom in the U.S. If they can do that, then sales (if not the price) of their product will rise in America again. If they can keep the price low, (they think) they can keep all those petrodollars flowing in their direction.
Thing is, they're so rich, they can afford the hit to their bottom line. They're willing to take it, too, if they can kill their competition.