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E and P Notes |
1 Petroleum Consultant, 1511 18th Avenue East, Seattle, Washington, 98112; scott.montgomery{at}prodigy.net
2 Geologist, Utah Geological Survey, 1594 West North Temple, Suite 3110, Salt Lake City, Utah, 84114-6110; nrugs.dtabet{at}email.state.ut.us
3 Geologist, U.S. Geological Survey, Building 20, MS 977, Denver Federal Center, Sixth Ave and Kipling Street, Denver, Colorado, 80225; barker{at}usgs.gov
Scott L. Montgomery is a petroleum consultant and author. He received his B.A. degree in English from Knox College in 1973 and his M.S. degree in geological sciences from Cornell University in 1978. He is widely published in the geosciences and since 1996 has been principal author of the E&P Notes series in the AAPG Bulletin. His other publications include seven books on topics in petroleum geology, science education, and the history of science, plus articles and monographs related to frontier plays, new technologies, field studies, and reservoir characterization.David E. Tabet is the acting head of the Economic Geology Program for the Utah Geological Survey. He holds B.S. and M.S. degrees in geology from the University of Wisconsin and an M.B.A. from the University of Colorado. He has worked for the New Mexico Bureau of Mines and Mineral Resources as a coal geologist, the ARCO Coal Company, clients as a consultant, and since 1992, the Utah Geological Survey.
Charles E. Barker has been a research geologist with the U.S. Geological Survey for 21 years. He was educated at San Diego State University (B.S. degree, 1974), University of California, Riverside (M.S. degree, 1979) and the University of Adelaide (Ph.D., 1995). His research has been on multiple thermal indicators to constrain burial history reconstruction of sedimentary basins, the geochemical evaluation of petroleum source rocks and coals, and using burial history and coal facies to predict coalbed gas content. Currently, he is involved in studies of Ferron Trend, Utah; Upper Cook Inlet, Alaska; and Wilcox coals, U.S. Gulf Coast. Foreign assignments for the U.S. Geological Survey include finding alternate energy sources in post-war Croatia, locating coalbed gas in Armenia to reduce dependency on nuclear power, and promoting CBM gas production in Colombia. Currently, Charley is chairman of the Coal Geology Division of the Geological Society of America. He has also served as the 1999 president of the Society for Organic Petrology, as delegate to the American Geological Institute Member Society Council, and is a past president of the Society for Luminescent Microscopy and Spectroscopy.
Recent drilling for coalbed gas in the Upper Cretaceous Ferron Sandstone Member of central Utah has resulted in one of the most successful plays of this kind. Exploration to date has resulted in three fields and a potential fairway 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 (CBM) 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 than 500 mcf/day and, after several years, continue to typically show negative 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 five 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 chronostratigraphy, the play is divided into northern and southern parts. The northern part is characterized by coals that have the following characteristics: (1) high gas contents; (2) moderate thermal maturity (e.g., vitrinite reflectance [Ro] values of 0.6-0.8%); (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 lower thermal maturity (Ro = 0.4-0.6%), and they are exposed along an extensive, 35 mi (56 km) outcrop belt that may have allowed a degree of flushing. These coals, however, are also thicker and more extensive than those to the north and thus may retain significant potential. Northern coals appear to contain a mixture of gas from three sources: in-situ thermogenic methane, migrated thermogenic methane from more mature sources, and late-stage biogenic gas. Current development is focused on the northern part of the stated fairway, where well control and an existing infrastructure are present. Indications are that CBM exploration in the Ferron will expand considerably in the near future.
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