They do not want to use up any gas pressurizing, or to be used to pressurize, Ghawar?
I see 300 tcf being way, way more gas than Ghawar could possibly utilize.
Besides, a lot of Ghawar is pressurized by water injection besides returning associated gas.
In time, CO2, not natural gas, will be the injection medium as recoveries will optimize from this giant field.
There are massive gas reservoirs such as the Khuff that are yet to be exploited underlying much of the ME including SA. I analyzed exploration of these in Kuwait, Qatar and UAE.