ABSTRACT
Until recently, many oil and gas companies considered natural gas locked in tight, impermeable shale uneconomical to produce. Advanced drilling and reservoir stimulation methods have dramatically increased gas production from unconventional shales. The Barnett Shale formation in Texas has experienced the most rapid development. The Marcellus Shale formation of the Appalachian basin, in the northeastern United States, potentially represents the largest unconventional gas resource in the United States. Other shale formations, such as the Haynesville Shale, straddling Texas and Louisiana, have also attracted interest, as have some formations in Canada. The resource potential of these shales has signicantly increased the natural gas reserve estimates in the United States (Andrews, 2009).
