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ROBERTS, STEPHEN B., and NEIL S. FISHMAN, U.S. Geological Survey, Denver, CO

ABSTRACT: Coal-bed Methane Potential In The Laramie Formation, Greater Wattenberg Area, Denver Basin, Colorado: Just Wishful Thinking?

The Gas Research Institute estimates that 2 trillion cubic feet of methane (inplace) is present in Cretaceous and Tertiary coal in the Denver Basin, Colorado. In the 2,900 mi2 greater Wattenberg area (GWA), potential coal-bed gas resources may exist in the Upper Cretaceous Laramie Formation, which overlies current gas production targets in older Cretaceous strata. In the GWA, commingled production from all Cretaceous units is allowed, and relaxed drill-spacing requirements (<40 acre spacing) may permit recompletion of wells to tap into additional pay zones. Could the Laramie Formation include such a pay zone?

In the GWA, the lower part of the Laramie Formation contains coal, with individual beds ranging from 2-14 ft thick; cumulative coal thickness can exceed 25 ft. The coal occurs at depths ranging from <200 ft to >1,300 ft. Heat-of-combustion values greater than 9,000 BTU/lb are reported for Laramie coal beds in the southwestern part of the GWA.

Current success in coal-bed methane production, including development in lowrank coal, suggests that it might be time to reconsider coal-bed methane development in the GWA. Although data related to coal-bed methane in the Laramie Formation are sparse, accounts of gas in mines that produced Laramie coal and methane occurrence in water wells penetrating coal beds may attest to a potential gas resource. Additionally, greater BTU values in coal from the southwestern GWA may relate to a thermal anomaly previously identified in the Wattenberg field, suggesting that coal rank (and methane potential?) may be enhanced in this area. If found viable, coalbed methane resources in the Laramie Formation could result in the growth of gas reserves by providing a shallow pay zone in new or existing gas wells.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico