Yes, this is a cheap visual metaphor. Photographer: David McNew/Getty Images
Yes, this is a cheap visual metaphor. Photographer: David McNew/Getty Images

It's not surprising that a survey of energy professionals attending the 2014 North American Prospect Expo overwhelmingly identified "U.S. energy independence" as the trend most likely to gain momentum this year. Like any number of politicians and pundits, these experts are riding high on the shale boom -- that catch-all colloquialism for the rise of hydraulic fracturing and horizontal drilling that have unleashed a torrent of hydrocarbons from previously inaccessible layers of rock.

But this optimism belies an increasingly important question: How long will it all last?

Among drilling critics and the press, contentious talk of a "shale bubble" and the threat of a sudden collapse of America's oil and gas boom have been percolating for some time. While the most dire of these warnings are probably overstated, a host of geological and economic realities increasingly suggest that the party might not last as long as most Americans think.

For the better part of two centuries, the American oil and gas industry drew its treasure from porous underground formations where hydrocarbons moved comparatively easily to the surface. The best of those resources began to dry up in the 1970's and imports began to rise. Enter hydraulic fracturing and horizontal drilling, technologies that allow developers to extract oil and gas from much deeper, tighter and far-less-porous rock formations, including shale.

The problems arise when you look at how quickly production from these new, unconventional wells dries up. David Hughes -- a 32-year veteran with the Geological Survey of Canada and a now research fellow with the Post Carbon Institute, a sustainability think-tank in California -- notes that the average decline of the world's conventional oil fields is about 5 percent per year. By comparison, the average decline of oil wells in North Dakota's booming Bakken shale oil field is 44 percent per year. Individual wells can see production declines of 70 percent or more in the first year.

Shale gas wells face similarly swift depletion rates, so drillers need to keep plumbing new wells to make up for the shortfall at those that have gone anemic. This creates what Hughes and other critics consider an unsustainable treadmill of ever-higher, billion-dollar capital expenditures chasing a shifting equilibrium. "The best locations are usually drilled first," Hughes said, "so as time goes by, drilling must move into areas of lower quality rock. The wells cost the same, but they produce less, so you need more of them just to offset decline."

That's a tall order when prices are low. Currently, natural gas is moving at about $4.50 per MMBtu -- a welcome uptick, but by no means ideal for producers. Even if that climbed to $6, Hughes estimates that shale gas growth would last only another four years or so, at which point even-higher prices would be needed to maintain production, let alone keep it growing.

Speaking last month to Oilprice.com, Art Berman, a Houston-based geological consultant with a similarly sober (and often unpopular) view of the shale boom, called for more realistic assessments of its longevity. "I'm all for shale plays, but let's be honest about things, after all," Berman said. "Production from shale is not a revolution; it’s a retirement party." Berman and Hughes both presented their concerns at the annual meeting of the Geological Society of America last fall.

Not everyone thinks this sort of pessimism is warranted. With funding from the Alfred P. Sloan foundation, Scott Tinker, a professor of geosciences at the University of Texas at Austin has been leading one of the most comprehensive, well-by-well analyses of the four biggest shale gas reserves in the U.S., including the contentious Marcellus formation in the Appalachians. Tinker doesn't quibble much with Hughes' and Berman's observations about well depletion rates, though he interprets the implications differently.

"Just like conventional drilling, the broad message here is that these basins are going to continue to be drilled and there will be money made by some and lost by others," Tinker said. He prefers to call the shale boom an evolution rather than a revolution, and he suggests that while new wells must consistently be plumbed to address the shortfalls of old ones, this has always been the case. Newer drilling technology that allows several well paths to proceed from a single surface installation will help minimize local impacts, Tinker says -- adding that with higher prices, the shale gas boom could remain healthy as far out as 2040.

That's not an immediate threat, but it's also not exactly the 100-years-of natural gas that President Barack Obama has touted. Clearly, neither shale oil production, which even Tinker concedes is likely to peak just five or six years from now, nor shale gas will escort the U.S. into the era of energy independence. Getting there requires a much more deliberate diversification of the nation's energy portfolio, along with far more aggressive efforts to increase efficiency and eliminate energy waste -- steps that, by the way, are also critical in addressing that other nagging issue, global warming.

To contact the editor responsible for this article: Tobin Harshaw at tharshaw@bloomberg.net.

To contact the writer of this article: Tom Zeller Jr. at tzeller@mit.edu.