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AAPG Bulletin


AAPG Bulletin, V. 87, No. 9 (September 2003), P. 1485-1507.

Copyright copy2003. The American Association of Petroleum Geologists. All rights reserved.

A geochemical perspective and assessment of leakage potential for a mature carbon dioxidendashenhanced oil recovery project and as a prototype for carbon dioxide sequestration; Rangely field, Colorado

Ronald W. Klusman1

1Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado; email: [email protected]


Ron Klusman received a B.S. degree in chemistry from Indiana University in 1964 and a Ph.D. in geology and geochemistry from Indiana University in 1969. During graduate studies, he was employed as an instrumental analyst at the Indiana Geological Survey. From 1969 to 1972, he was an assistant professor of geosciences at Purdue University. From 1972 to 2001, he was associate professor and professor of chemistry and geochemistry at the Colorado School of Mines, retiring in 2001. The Rangely research culminates an extensive research record in soil gas, and the Rangely work was primarily done in retirement.


This research was supported by the U.S. Department of Energy under Grant No. DE-FG03-DOER15090 to the Colorado School of Mines. Advice and cooperation of many individuals at the Colorado School of Mines and Chevron U.S.A. Production (Chevron-Texaco) were critical in making this research possible.

I thank Kent Bowker, Janell Edman, and Dietmar Schumacher for their reviews and comments that resulted in a greatly improved manuscript.


Measurements of CO2 and CH4 soil gas concentrations and gas exchange with the atmosphere at a large-scale CO2-enhanced oil recovery (EOR) operation at Rangely, Colorado, United States allowed assessment of the microseepage potential. Shallow and deep soil gas concentrations and direct transport of CO2 and CH4, complemented by carbon isotopes, have demonstrated an estimated microseepage rate to the atmosphere of approximately 400 t CH4/yr from the 78-km2 area of the Rangely field. Preliminary estimates of deep-sourced CO2 losses are in the range of 170 to less than 3800 t/yr. Several holes as much as 9 m deep for nested sampling of gas composition, stable carbon isotopic ratios for CO2 and CH4, and carbon-14 measurements on CO2 indicate that deep-sourced CO2 microseepage loss was detected. Methanotrophic oxidation of microseeping CH4 to CO2 in soils demonstrates significant contribution to soil gas CO2 in high CH4 flux areas, necessitating a revision of the estimated direct CO2 microseepage rate to less than 170 t/yr over the Rangely field.

An evaluation of produced water quality from pre-CO2-EOR to 1999 demonstrates an increase in some parameters, particularly of Ca2+ and HCO3minus, indicating dissolution of ferroan calcite and ferroan dolomite in the Weber Formation. Inverse computer modeling suggested carbonate mineral sequestration was possible within the constraints of evolution of produced water quality. X-ray analyses of well scales, however, do not support the presence of significant mineral sequestration. Instead, modeling indicates that the bulk of the CO2 that has been injected since 1986 is sequestered as dissolved CO2.

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