Good news in that new investments must be made to extract more....

Good news in that new investments must be made to extract more. The current wells can't just have its tap turned.

So while they can tap nearby reserves, the Saudis are betting that new spend on new greenfield, most of which will probably have to come from offshore, will have to be made. This construction would take some time to bring oil online... enough for them to make decent profit from higher oil prices.