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EIA: Shale Gas Reserves Numbers 'Work in Progress'

July 30, 2012
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The U.S. Energy Information Administration (EIA) said last week U.S. shale formations are estimated to contain 483 Tcf of unproved technically recoverable natural gas and 33.2 billion bbl of unproved technically recoverable tight oil, numbers that closely mirror figures published in January.

The EIA conceded that its estimates of technically recoverable resources (TRR) are a "work in progress" that evolves with production technology but added that the biggest unknown involved the estimated ultimate recovery (EUR) per well.

In January the EIA's Annual Energy Outlook 2012 (AEO2012) stated that unproved TRR for natural gas in the United States were 482 Tcf, down substantially from the 827 Tcf estimate of AEO2011 (see NGI, Jan. 30). The Marcellus Shale made up 141 Tcf of the overall figure.

With its latest estimate, the EIA said the Marcellus Shale still holds 141 Tcf of unproved technically recoverable natural gas. The Haynesville/Bossier Shale held the second-highest amount of gas at 66 Tcf, followed by the Eagle Ford at 60 Tcf. The other shale plays mentioned were the Utica (16 Tcf), Fayetteville (13), Woodford's Anadarko and Arkoma formations (both at 11), Pearsall (9), Chattanooga (2), and Caney (1). All other U.S. shale plays accounted for an estimated 163 Tcf.

For unproved technically recoverable tight oil, the EIA estimated that the Monterey/Santos Shale in California held 13.7 billion bbl, followed by the Niobrara formation with 6.5 billion bbl and the Bakken/Sanish/Three Forks with 5.4 billion bbl. Other shale formations that held significant tight oil resources included the Austin Chalk (2.7 billion bbl), Eagle Ford (2.5 bbl), Avalon's Bone Springs formation (1.6 billion bbl), Spraberry (510 million bbl) and Woodford's Anadarko formation (393 million bbl).

The EIA said uncertainty over calculating the EUR per well was compounded by the fact that most unconventional gas and tight oil wells were only a few years old and their long-term productivity is untested. Another factor complicating the issue is the fact that companies have already targeted the "sweet spots" of shale plays.

Earlier this month the EIA said it was forecasting a small drop in natural gas production over the next several months (see NGI, July 16). But it also forecast an increase in natural gas production every year through 2035 because of the unconventional plays, whose resources have expanded through unconventional drilling technology (see NGI, July 2).

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