See US May Hold Large Reserves of Shale Oil, but is it Economically Out of Reach?
The problem with fracked wells is that production drops off extremely fast, at an average of about 80% in the first year in gas wells according to exhaustive studies by Schlumberger and University of Oxford, and somewhat less than 80% in shale oil wells. The declines are gradual in later years.Initial drilling costs are very high and to maintain production,wells have to be refracked.
Fracking is akin to a person running hard on a fast treadmill just to stay in the same spot! The US should not bet its energy future on it.