My understanding is that the microwaves are only used to break the initial stone to get to the oil. I don’t think they are microwaving cubic miles of stone for its oil.
Here’s what the article says:
“Scientists believe they can transmit microwave energy down a shaft and into the ground to zap oil shale deposits with energy, heating them up. Using microwaves to cook oil shale would cause the petroleum to condense and boil to the surface without high-pressure injections... as the heat drives oil to the surface, ‘the rock basically becomes transparent’ to the microwave beam, enabling it to penetrate deeper.”
The article is “New Microwave Technology May Out-frack Fracking.”
Perhaps it’s posted at the newsmax.com website. I was too lazy to check. I have the magazine and typed the above quote (whch was more work than linking duh).