That has a bit of a 'tin foil hat' ring to it. How about this alternate wording:
not to use them until "the cost of oil had risen to such a level that they could justify the much higher extraction costs"
We are nearing or at that point today, as witness the developments in Alberta. I would guess we are 5-10 years away from serious development in shale oil extraction.
I've grown up in the oil industry and such an area. San Juan county gives the USA huge chunk of natural gas.
From time to time I've ran across folks in the industry who have been in a position to know. They've affirmed such a deliberate secret locking away of oil resources to varying degrees.