Upper Cretaceous Ferron Sandstone: Major coalbed methane play in central Utah

Recent drilling for coalbed gas in the Upper Cretaceous Ferron Sandstone Me mber of central Utah has resulted in one of the most successful plays of th is kind. Exploration to date has resulted in three fields and a potential f airvay 6-10 mi (10-16 km) wide and 20-60 mi (32-96 km) long, corresponding to shallow coal occurrence at depths of about 1800-3500 ft (545-1060 m) in the Ferron, a sequence of interbedded fluvial-deltaic sandstone, shale, and coal in the lower part of the Cretaceous Mancos Shale. Coalbed methane (CB M) reservoirs in this interval consist of thin to moderately thick (3-10 ft [1-3 m]) coal beds of relatively low rank (high-volatile B bituminous) and variable gas content, ranging from 100 scf/ton or less in the south to as high as 500-600 scf/ton in the north. Productive wells have averaged more t han 500 mcf/day and, after several years, continue to typically show negati ve production declines. In the major productive area, Drunkards Wash unit, the first 33 producers averaged 974 mcf and 85 bbl of water per day after f ive years of continuous production. Estimated ultimate recoverable reserves for individual wells in this unit range from 1.5 to 4 bcf. Based on several criteria, including gas content, thermal maturity, and chr onostratigraphy, the play is divided into northern and southern parts. The northern part is characterized by coals that have the following characteris tics: (1) high gas contents; (2) moderate thermal maturity (e.g., vitrinite reflectance [R-o] values of 0.60-0.8%); (3) good permeabilities (5-20 md); (4) lack of exposure; and (5) overpressuring, due to artesian conditions. Southern coals have much lower average gas contents (<100 scf/ton) and lowe r thermal maturity (R-o = 0.4-0.6%), and they are exposed along an extensiv e, 35 mi (56 km) outcrop belt that may have allowed a degree of flushing. T hese coals, however, are also thicker and more extensive than those to the north and thus may retain significant potential. Northern coals appear to c ontain a mixture of gas from three sources: in-situ thermogenic methane, mi grated thermogenic methane from more mature sources, and late-stage biogeni c gas. Current development is focused on the northern part of the stated fa irway, where well control and an existing infrastructure are present. Indic ations are that CBM exploration in the Ferron will expand considerably in t he near future.