The expanded use of horizontal drilling and the advent of hydraulic fracturing helped Pennsylvania more than quadruple its natural gas production between 2009 and 2011, according to the U.S. Energy Information Administration (EIA).

Prior to 2009 natural gas exploration and development activity in Pennsylvania was relatively steady, with operators drilling a few thousand conventional wells each year which produced 400-500 MMcf/d, EIA said.

“With the shift to and increase in horizontal wells, however, Pennsylvania’s natural gas production more than quadrupled since 2009, averaging nearly 3.5 Bcf/d in 2011. Natural gas wells accounted for virtually all (99%) of the horizontal wells started over this period,” the agency said.

Most conventional drilling traditionally took place in western Pennsylvania, but horizontal drilling has been spread over a wider area, stretching from the southwest corner of the state to the northeast to tap into the Marcellus, Utica and Geneseo/Burket shale formations. The number of vertical wells — which are typically less productive — fell as the number of horizontal wells ballooned, resulting in an overall decline in the state’s well count, EIA said.

Low natural gas prices have also held down the well count, the agency said. During the first four months of 2012 drilling began on 618 new natural gas wells in the state, an 82-well decline compared to the 700 wells started during the same period in 2011.

“In contrast, 263 new oil and ‘combination’ (oil and natural gas) wells were started in Pennsylvania from January through April 2012, well above the 164 new wells that began drilling during the corresponding period in 2011,” EIA said.

The EIA web-based report on the Marcellus includes an animated map that shows the progression from vertical wells to horizontal wells from January 2005 through April 2012.

Due mainly to drilling in the Marcellus Shale, Pennsylvania’s marketed gas production last year more than doubled to nearly 1.3 Tcf, according to preliminary estimates from Pennsylvania’s Department of Environmental Protection (see Shale Daily, April 30). Marketed natural gas production of the top-five producing states — Texas, Louisiana, Wyoming, Oklahoma and Colorado — grew 7.5% last year, but their combined share of U.S. gas output fell slightly to about 65%, reflecting increased contributions from other states, particularly those in which operators significantly expanded development of shale gas formations, according to EIA.

Domestic gas production reached an all-time record in 2011, surpassing levels last seen in the 1970s, according to a recent market report by the Federal Energy Regulatory Commission’s Office of Enforcement (see Shale Daily, April 20). Dry gas shales, such as the Haynesville in Louisiana, the Fayetteville in Arkansas and the Barnett in Texas, remained the largest producing shales in 2011. However, the fastest growing shales were found in the liquids-rich shale basins, such as the Marcellus, the report said.