It’s a brave new world for U.S. shale gas. Industry groups, academics and financial analysts have joined the chorus singing the praises of this clean, domestic and abundant energy source that has emerged in the past few years.

And yet, there are some voices crying in the wilderness. Shales are not all they seem; the hype is overblown; the estimates of potential reserves are wildly optimistic.

It’s good to consider all arguments, and we all know that statistics can be pushed and pulled to fit various scenarios.

Analysts at Calgary-based Ross Smith Energy Group have taken a hard look at the economics and resource potential in the best areas of known shale plays. Manuj Nikhanj and Salim Jamal recently released a study that concluded that North America’s eight largest shale plays hold some 475 trillion cubic feet of recoverable resources—just in their core areas.

That’s a lot of natural gas. The Barnett shale, the granddaddy of modern shale plays, supplies almost 10% of Lower 48 gas production from an available resource base a tenth that size.

The Ross Smith analysts are careful to note that the presence of shale does not automatically ensure economic success. It’s all location, location, location. Within each shale play there are areas that can deliver gas at commodity prices as low as $4 per thousand cubic feet, but there are also huge areas of the same play that are subeconomic below $10.

The analysts figure there are some 13.6 million core acres in the Barnett, Woodford, Fayetteville, Marcellus, Haynesville, Montney, Horn River and Eagle Ford plays, and between 40% and 75% of that total can be viably developed.

These core regions could support some 128,000 additional wells, beyond the mere 7,800 horizontal core wells that have already been drilled. So the size of the prize is stunning.

Finding and development costs within the best areas of the Big 8 plays range from $1.43 per thousand in British Columbia’s Montney to $2.84 in Oklahoma’s Woodford. And according to the Ross Smith analysts, median well results deliver a 40% lower breakeven cost in the core than in noncore areas.

Shale plays, at least the newly discovered ones, don’t have a lot of history. Ross Smith analyzed average well productivity in the core areas in the Barnett, Woodford and Fayetteville, the most established of the group. Each play shows a robust decline curve in the first year.

To date, some 8,400 horizontal wells have been drilled in the Barnett shale, and 5,800 of those are in the core area. The median well productivity in the core is twice that of the noncore area.

In the Fayetteville, about 1,300 horizontal wells have been drilled, and 1,050 of those are in the core. In this play, core wells are 2.5 times more productive than noncore wells.

The Woodford sports 800 horizontal wells, and 550 of those are in the core. As in the Barnett, the core wells are twice as productive as noncore wells.

What’s remarkable about the three plays is that 85% to 90% of all the gas produced in each play flows from their core areas. It really matters where you are in a shale play, just as it has always mattered in conventional drilling.

It’s important to note that well results are widely distributed. Although shales are often called “gas-factory plays,” in reality individual well results vary significantly. But, per-well estimated ultimate recoveries within the Barnett, Woodford and Fayetteville cores are around 2 billion cubic feet (Bcf).

“In an unrestricted world, shale gas could single-handedly supply all additions needed to keep North American gas supply flat,” says Nikhanj. The production base in the U.S. and Canada declines at 28% and 22%, respectively, so the industry needs to replace anywhere from 17 to 19 Bcf per day to keep production flat. Shales have the capability to supply that gas. In reality, there are limits on the pace of development, including infrastructure, operators’ opportunity sets and the number of operators active in a play.

“A huge percentage of future production additions will come from shale resources,” he says. “This will work to flatten and reduce the supply-cost curve.”