Over his 55-year career, Henry Groppe has a reputation for being ahead of the curve, and for being right more often than wrong. Yet when the renowned energy forecaster confidently proclaimed natural gas prices will double in the next 12 to 18 months, a buzz of disbelief—even laughter—pervaded the august hall brimming with energy movers.

That's because the call is in such stark contrast to the decidedly bearish sentiments of most oil and gas prognosticators, who believe the flood of gas from shale resources will depress prices for a long, long time.

Groppe, the iconic head of consulting firm Groppe Long & Littell, established in 1955, revealed his contrarian outlook to 450 austere and startled oil and gas executives at Hart Energy's Energy Capital Conference in Houston.

"Within the next 12 to 18 months, we will see prices of natural gas in the U.S. roughly doubling," predicted Groppe. "Our anticipation is that gas prices will be on the order of $9 to $10 a year from now."

Ten bucks. Next year. Even as natural gas prices have approached a distantly remembered $5 per thousand cubic feet over the past few weeks, no one seemingly can believe such an increase is possible in the current gas-glut environment.

Groppe's argument is layered, but simple: Supply will not meet demand. Here's why.

Conventional gas production from the Lower 48 and Gulf of Mexico has been and remains in long-term decline. Two unconventional resources have offset that supply decline over the past 25 years—tight gas and coalbed methane. But significantly, both of those peaked in 2008 and are declining at rates you would expect with such resources. Together, these sources contribute some 45 billion cubic feet (Bcf) of the total 65 Bcf of domestic supply, and are trending down sharply.

"That's a very important internal dynamic change," stated Groppe. "That means going forward, there's a much, much steeper hill to be climbed by growing shale-gas production."

The difference lies in the 15 Bcf currently contributed from shales. "At the top of the total projected gas supply, you see the differential that would have to be met by continually growing shale-gas production to hope to have a balanced supply," Groppe said. "We doubt very much that that will occur."

In fact, Groppe has no confidence that shale-gas production will be anywhere near euphoric predictions—it will be far less than industry anticipates, he warns.

A couple of reality checks. Groppe reminded the audience that CBM projections were similarly hyped 25 years ago, when economically recoverable coalbed reserves were estimated at 500 trillion cubic feet (Tcf).

"The potential of coalbed methane looked a lot like the discussion of the shale potential today. We had coalbeds all over the country that were cheaply cored. The methane was there. We had the new technology, the tax incentives." Cumulative production to date? Just 25 trillion.

He compares that with the Barnett shale as a test case, where 50 years of legacy production and 11,000 wells painted a uniquely detailed picture of the reservoir qualities. Now, 15,000 horizontal wells later, Barnett production has plateaued at 5.5 Bcf per day, with 8 Tcf cumulative. A warning sign.

"We find this comparison over and over again of the anticipation at the beginning versus what it's like 15 to 25 years later, after you have had the production history, experience and the economics to see how these new resources turn out."

Groppe is likewise skeptical of stats indicating a growing gas supply. Since the first of the year, gas inventories have been steadily declining. "We're now at about 250 billion in five months below the same point we were last year. That raises caution flags about what is really happening to total gas production related to supply."

Instead, liquified natural gas imports will remain a necessary source of future supply, he anticipates, up to 3.5 Bcf per day from 1.5 to 2 Bcf per day now.

Has the tide already turned? In April, for the first time since 1995, the gas rig count crossed below the buoyant oil rig count, continuing its downward momentum. Process through a few thousand gas wells waiting on completion, drill less, and flush shale-gas production could tip over, as Groppe projects.

But, alas, all is not bullish in Groppe's five-year forecast. In response to favorable prices, producers will be enticed back into the gas markets, including CBM, and overdo it, he said. "We'll probably have a surplus again