-- John Kemp is a Reuters columnist. The views expressed are his own --

LONDON, Nov 11 (Reuters) - Nothing illustrates technology’s power to transform the energy outlook more clearly than the development of the Barnett shale gas deposit under the city of Fort Worth in Texas. [ID:nLB663660]

The resulting increase in U.S. gas output has made a decisive contribution to the “unexpected boom” in North American gas production and the emergence of a worldwide “gas glut,” cited by the International Energy Agency (IEA) in its World Economic Outlook (WEO).

It may be hard to remember now, but it is less than five years since the Hirsch Report, prepared for the U.S. Department of Energy, warned that previous optimism about gas supplies “turns out to have been misplaced” and “supply difficulties are almost certain for at least the remainder of the decade.”

"Gas production in the United States now appears to be in permanent decline," according to senior analysts cited in the report. Hirsch urged policymakers to learn lessons from "peak gas" and be ready to deal with the disruption caused by "peak oil" (here).

Instead, dry gas production has soared from 18.5 trillion cubic feet (tcf) in 2005 to 20.4 tcf in 2008, and is on course to hit 21 tcf in 2009 (the highest since 1973-74).

Much of the surge has come from rapid growth in shale gas. While total U.S. gas production rose 1,288 billion cubic feet (bcf) between 2007 and 2008 (6.7 percent), the shale component leapt by 838 bcf (70 percent) and accounted for two-thirds of total growth.

BARNETT AND OTHER PLAYS

Shale resources are enormous. Proven reserves stood at 32.8 tcf in 2008, according to the U.S. Energy Information Administration (EIA). But the total recoverable resource is estimated AT 600-750 tcf, distributed widely across the continental United States. (here)

Several big shale plays are being developed, including Marcellus in the Northeast and Appalachia; Fayetteville in Arkansas-Oklahoma; and Haynesville in northern Louisiana-eastern Texas. But the biggest development has been Barnett in North Texas. (here)

Barnett production soared from 380 bcf in 2004 to 1,563 bcf in 2008, according to the Texas Railroad Commission (TRC) which regulates the industry, and is still climbing.

Between 2007 and 2008, increased output from Barnett (481 bcf) accounted for more than a third of the increase in all natural gas production nationwide. Barnett’s development is probably the single most important factor confounding predictions of a gas peak.

It is not even the largest potential play (Marcellus and Haynesville are each thought to have more than five times as much recoverable gas). Barnett was merely developed first. The IEA has called it the “birthplace of the revolution.”

What makes Barnett extraordinary is that the counties at the play’s “core” (Wise, Tarrant, Johnson and Denton) include some heavily built up urban areas, including a part of the Dallas-Forth Worth metroplex. Vast quantities of gas are being extracted from directly beneath a city.

Barnett had a total of 12,135 wells at the start of September 2009 according to the TRC. (here) Many were drilled in urban environments. (here).

TECHNOLOGY CHALLENGES

Extracting gas from shale presents formidable technical challenges:

(1) Shale formations and gas resources are widely distributed (so the risk of drilling a completely dry well is lower) but the gas is less concentrated than in conventional fields (so many more wells have to be drilled to obtain the same amount of gas).

(2) In a conventional oil or gas field, hydrocarbons are held in a porous reservoir rock and “flow” to the bottom of the well, initially under natural field pressure, later supplemented by the injection of water or other fluids to maintain as natural pressure falls. But shale is not porous so gas does not naturally flow towards the well.

In fact, shale is so impermeable it often forms the “cap” over the top of conventional gas and oil reservoirs that prevents conventional hydrocarbons escaping to the surface and allows them to be recovered in commercial quantities. In some instances, the “new” shale fields actually lie on top of conventional gas and oil reservoirs. Wells have already been drilled down through the shale to access the conventional gas and oil beneath.

(3) Shale production brings vast amounts of briny water to the surface which must be disposed of without ruining local drinking water supplies.