Coalbed natural gas (CBNG) production from the prolific Powder River Basin (PRB) in Wyoming hit a new record in 2009, fueled by the output from the Big George coal seam, the Wyoming State Geological Survey (WSGS) reported.

PRB output last year topped 558 Bcf of natural gas, even though there were fewer producing wells compared with 2008, said state officials.

“The Powder River Basin CBNG play is the largest natural gas producing area in Wyoming,” said WSGS geohydrologist Scott Quillinan.

Since drilling ramped up in 1987, nearly 3.7 Tcf of CBNG has been produced from the basin, enough gas to meet the needs of about four million homes for 10 years.

“At the beginning of 2009, approximately 27,000 wells had been drilled in the basin, of which about 17,000 were producing and 10,000 were shut in,” said Quillinan. “During the year, the number of producing wells had decreased by nearly 3,500. Despite this drop, 2009 proved to be the largest production year to date.”

Also factoring into higher gas production is the “strong likelihood” that many of the wells shut in 2009 were not big producers, said officials.

In addition to more gas output, another record also was achieved in 2009: the lowest water-to-gas ratio since drilling in the PRB began. About 1.02 bbl of water was produced for every Mcf of gas, based on 42-gallon bbl of water. Water production in the basin dropped last year by 17% to 566 million bbl from 681 million bbl.

To date, 6.076 billion bbl of water has been pumped from PRB coal seams, or 783,092 acre-feet of water, according to the WSGS. Water in coal seams has to be pumped to the surface to lower the formation pressure and release natural gas.

“The water-to-gas ratio for the Powder River Basin continues to decrease,” Quillinan said. “In 2000, the ratio was nearly 2.5 bbl/Mcf of gas. It had decreased to 1.7 by 2005, and next year it may dip below 1.0.” The trend is expected to continue as the coal beds are depressurized.

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