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

¹ Shell Exploration and Production Company, BTC, P.O. Box 481, Houston, Texas 77001; etuan.zhang{at}shell.com
² Geology Program, Western State College, Gunnison, Colorado, 81230; rhill{at}western.edu
³ Chevron Corporation, Energy Technology Company, Houston, Texas 77002; barrykatz{at}chevron.com
⁴ Petroleum Energy and Environment Research Center, California Institute of Technology, Covina, California 91722; tang{at}peer.caltech.edu

Etuan Zhang received his Ph.D. from Pennsylvania State University. He has more than 14 years of industrial experience in petroleum exploration and production research. His research interests include petroleum system analysis, basin modeling, source rock pyrolysis and reaction kinetics, and investigation of unconventional resources.

Ronald Hill specializes in petroleum geochemistry and has more than 12 years of oil industrial and government experience. Currently, he occupies the Moncrief Chair in Petroleum Geology at Western State College in Gunnison, Colorado. His research interests include shale-gas resources and processes that control petroleum generation. Ron holds geology degrees from Michigan State University (B.S. degree) and the University of California, Los Angeles (Ph.D.), and a geochemistry degree from the Colorado School of Mines (M.S. degree).

Barry Jay Katz received his B.S. degree in geology from Brooklyn College and his Ph.D. in marine geology and geophysics from the University of Miami. He has held various technical and supervisory positions in Texaco's, ChevronTexaco's, and Chevron's technology organizations since joining Texaco in 1979. Barry is currently a Chevron Fellow and team leader for the hydrocarbon charge in Chevron's Energy Technology Company.

Prior to joining the California Institute of Technology, Tang had more than 15 years of industrial experience in both upstream and downstream research at Chevron. He is currently the director for the Petroleum Energy and Environment Research Center at the California Institute of Technology. Tang has published more than 80 articles in the field of geochemistry, chemistry, and petroleum engineering. His major research interests are applying molecular modeling and experimental simulation techniques to energy-related problems. He has pioneered the molecular modeling technique to many fields of organic geochemistry, surface chemistry, reaction kinetics, and other petroleum chemistry fields. Tang feels that the major technical barrier of molecular modeling for the petroleum industry is the lack of integration between theory and experiments. Thus, his research group has a strong integration of modeling and experimental efforts. His main research focuses are (1) modeling both homogenous and heterogeneous catalysis; (2) geochemical modeling; (3) interfacial phenomenon modeling (liquid-liquid, liquid-solid, and gas-solid); (4) the nucleation process; (5) emulsion; and (6) ionic liquids.

ABSTRACT

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 (R_o) changes were calculated from pyrolysis data. Experimental R_o results from this study are not adequately predicted by published R_o kinetics and indicate the necessity of deriving basin-specific kinetic parameters when building predictive basin models.

Using derived kinetics for R_o 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% R_o are about 300 standard cubic feet per ton (scf/ton) and more than 2500 scf/ton (in-situ dry-ash-free coal) at R_o values reaching 1.9%. Gases generated in both low- and high-maturity coals are less wet, whereas the wetter gas is expected where R_o 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.