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Abstract

Upper Cretaceous coals within the Ferron Sandstone Member of the Mancos Shale contain large volumes of coalbed methane. Coals at the northern end of the 80-mi (129 km)-long Ferron trend have produced 469 bcf of coalbed methane, as of the end of July 2003. At that time, 735 wells were producing 275 mmcfd. Analysis of cores from exploratory wells indicate that the gas content of the coals decreases dramatically from north to south, even though the rank and maturity of the coals decreases only slightly. The area with lowest gas content correlates with the outcrop of the Ferron coals in the southern portion of the trend. Hydrodynamic studies have shown that the Ferron coals are aquifers that are recharged from the Wasatch Plateau to the west. Regional mapping indicates that the productive fields are large stratigraphic traps in the central and northern part of the trend where the coals pinch-out updip into tight marine shales to the east. Much of the produced gas is secondary biogenic gas and migrated thermogenic gas that has moved from the Wasatch Plateau and south margin of the Uinta Basin, respectively. In the southern part of the trend, near the town of Emery, coals are present at the surface, but most of the gas has been flushed out of the coals due to reduction of reservoir pressure and active water flow from the west. Therefore, the entire Ferron trend probably contained tremendous volumes of stratigraphically trapped coalbed methane before uplift and erosion exposed the southern coals to the atmosphere.

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