The U.S. has exploited shale gas reserves. The U.S. had known about shale oil and gas since 1910.
According to the U.S. Energy Information Agency Australia has 396 trillion cubic feet (tcf) of recoverable shale gas. To put that in perspective China used around 4.4 tcf of natural gas last year.
By comparison the U.S. uses around 22 tcf per year.
Assuming most gas exports will go to China Australia has almost a 100-year supply of gas. That’s based on China’s current usage.