Antero Resources announced Monday that its proved reserves had increased 73% in one year by the end of 2012, while its proved, probable and possible (3P) reserves had increased 94% and its natural gas liquids (NGL) reserves increased by 170% during the same time frame, all thanks to discoveries in the Marcellus and Utica shale plays.

The Denver-based company said proved reserves totaled 4.9 Tcfe as of Dec. 31, 2012, pro forma for the sale of its assets in the Arkoma and Piceance basins. Meanwhile 3P reserves totaled 26.1 Tcfe — including 21.2 Tcfe in the Marcellus and 5.0 Tcfe in the Utica — and NGL totaled 1.6 billion bbl.

Last November, Antero sold all of its assets in the Piceance Basin — 61,000 net acres and 30 miles of gathering pipeline in western Colorado — to an undisclosed buyer for $325 million (see Shale Daily, Nov. 6, 2012). Five months earlier, Antero sold its acreage in the Arkoma Basin — 66,000 net acres in the Woodford Shale in Oklahoma, and 5,300 net acres in the Fayetteville Shale in Arkansas — to Vanguard Natural Resources LLC for $445 million (see Shale Daily, June 5, 2012).

Both deals made Antero a purely Appalachian Basin shale producer. By Antero’s calculation, the deals also reduced its year-end proved reserves by almost 2.2 Tcfe.

Antero said the Marcellus — where it holds 295,000 net acres — accounted for 97% of its proved reserve volumes, and 21% of its leasehold was classified as proved. The Utica accounted for the remaining 3%. The company said 75% of its proved reserve volumes were natural gas, 24% were NGL and 1% was crude oil.

“Given Antero’s successful drilling results to date, as well as those of other operators in the vicinity of Antero’s leasehold, the company believes that a substantial portion of its Marcellus Shale acreage will be added to proved reserves over time as more wells are drilled,” Antero said. The company drilled 61 wells targeting the Marcellus in 2012, with an average estimated ultimate recovery (EUR) of 11 Bcfe and an average lateral length of 7,381 feet.

Antero said it added 2.0 Tcfe of proved reserves through the drill bit in 2012, including 106 million bbl of NGL and 3 million bbl of crude oil, primarily in the Marcellus. Another 123 Bcfe of proved reserves in the Utica were added in the extensions category based on the success of early stage drilling there (see Shale Daily, Aug. 16, 2012). The company said another 324 Bcfe were added to proved reserves thanks to improved drilling techniques in the Marcellus, but 102 Bcfe were subtracted due to lower prices for natural gas and NGL.

On its 26.1 Tcfe of 3P reserves, Antero said they included 16.0 Tcf of natural gas, 1.6 billion bbl of NGL and 55 million bbl of oil. The company said NGL and oil collectively accounted for 38% of 3P reserves.

Antero said 94% pro forma of the increase in its 3P reserves were primarily driven by its addition of 84,000 net acres in the Marcellus, and 73,000 net acres in the Utica — in northern West Virginia and eastern Ohio, respectively — through acquisition and leasing.

The company said it has hedged 810 Bcfe of future production using fixed price swaps for the next six years — from Jan. 1, 2013 through December 2018, at an average NYMEX-equivalent price of $4.98/MMbtu. More than 65% of Antero’s estimated 2013 natural gas production is hedged at a NYMEX-equivalent price of $4.99/MMbtu.