No single day seems to go by without praises of the shale revolution. And no assessment of the oil market seems to work anymore without including the U.S. as a global supplier. If it continues like that, the International Energy Agency forecasts the U.S. will be a net exporter by 2030 and overtake Saudi Arabia by 2020. Unusual then to hear a bashing critique by one of the leading experts in the field, Andy Hall. Hall, who is also called the "oil guru" or "God" and earned a $100 million salary at Citigroup in the 2000s, said the recent decline in shale output is "likely [to] mean that the bounty afforded by shale resources is temporary."

Can that be true? Indeed, Hall is not the only one. Art Berman, head of a Houston-based geological consulting firm, states the majority of companies in the shale business are losing money due to overproduction depressing prices. In turn, drilling activity declined.

The same with a new study with the ironic title "Drill, Baby, Drill" by David Hughes. In the study, the independent geologist predicts a dim future of the shale industry and the reasons for that are twofold. Firstly, shale gas and oil wells deplete too quickly, while the best fields have been tapped and no major field discoveries are to be expected. Secondly, he concludes that although oil shales exist in vast deposits, their exploitation is still too expensive — so "the big tanks of these resources are inherently constrained by small taps."

But that's not the only thing. His study also shows operators overestimate actual well production on shale plays by a minimum of 100 percent and in some cases by up to 500 percent. (Note: A shale play is an area of land that companies believe to be productive.)

Have investors only been dreaming of a large shale yields then? Not quite true. The reality is not always as black and white. And the right thing to say might be that the industry was always very pragmatic about the downside of its business. This is at least what Terry Engelder, a professor at the Pennsylvania State University, said in an interview with Alternet, when stating the "industry's economic models where always based on those decline rates."

In the end, one should also not forget new facts supporting the revolution. For instance, a recent analysis by the U.S. Geological Survey just doubled previous estimates of how much oil is under North Dakota — up to 7.4 billion barrels, which would make it the largest oil field in the U.S. Further, steady technological improvements might make production less expensive in the near future (such as a technology recently developed that enables hydraulic fracturing equipment to be run by natural gas instead of diesel.)

On the other hand, while low natural gas prices might now be a reason for declining production — this does not always have to be the case. There are margins for natural gas prices to rise, for instance if it will be exported. And the likelihood for this to happen is not that small.

What I can conclude from this is revolutionary expectations in shale should be tempered. But they should not be discarded completely.