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AAPG Bulletin


AAPG Bulletin, V. 92, No. 8 (August 2008), P. 1077-1106.

Copyright copy2008. The American Association of Petroleum Geologists. All rights reserved.


Modeling of gas generation from the Cameo coal zone in the Piceance Basin, Colorado

Etuan Zhang,1 Ronald J. Hill,2 Barry J. Katz,3 Yongchun Tang4

1Shell Exploration and Production Company, BTC, P.O. Box 481, Houston, Texas 77001; [email protected]
2Geology Program, Western State College, Gunnison, Colorado, 81230; [email protected]
3Chevron Corporation, Energy Technology Company, Houston, Texas 77002; [email protected]
4Petroleum Energy and Environment Research Center, California Institute of Technology, Covina, California 91722; [email protected]


The gas generative potential of the Cretaceous Cameo coal in the Piceance Basin, northwestern Colorado, was evaluated quantitatively by sealed gold tube pyrolysis. The H/C and O/C elemental ratios show that pyrolyzed Cameo coal samples follow the Van Krevelen humic coal evolution pathway, reasonably simulating natural coal maturation. Kinetic parameters (activation energy and frequency factor) for gas generation and vitrinite reflectance (Ro) changes were calculated from pyrolysis data. Experimental Ro results from this study are not adequately predicted by published Ro kinetics and indicate the necessity of deriving basin-specific kinetic parameters when building predictive basin models.

Using derived kinetics for Ro evolution and gas generation, basin modeling was completed for 57 wells across the Piceance Basin, which enabled the mapping of coal-rank and coalbed gas potential. Quantities of methane generated at approximately 1.2% Ro are about 300 standard cubic feet per ton (scf/ton) and more than 2500 scf/ton (in-situ dry-ash-free coal) at Ro values reaching 1.9%. Gases generated in both low- and high-maturity coals are less wet, whereas the wetter gas is expected where Ro is approximately 1.4–1.5%. As controlled by regional coal rank and net coal thickness, the largest in-place coalbed gas resources are located in the central part of the basin, where predicted volumes exceed 150 bcf/mi2, excluding gases in tight sands.

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