In that context, not just increasing oil supply but reducing demand via changing fuels used by many, your number in today's dollars may be correct but I believe it will take decades.
Unless the gas is converted economically to a gasoline replacement without modification of the vehicle engines, the change over to natural gas will take decades. There are far too many gasoline engine vehicles that are not going to be replaced in ten years. Even if the supply of CNG service stations and vehicles became abundant, most people could not afford the switch without getting value for their current vehicle or continuing to run it until it dies.
If everyone wants a CNG car, who will buy your used gasoline car? How fast would a significant portion of the US ~250 million autos be replaced? Maybe 100 months to replace a 1/3 of them?
You can already buy conversion kits all day long.
Looks like a potential cottage industry either installing the kits or selling turnkey converted used cars.
That is the grey area......how rapidly will CNG be adopted.
It is looking very promising here in the Marcellus/Utica as many cities have committed to slowly convert their bus/trash/snow vehicles to CNG. Many local delivery groups have done the same for their trucks.
But, you are correct. Time will tell.