HR: 16:00h
AN: GC54A-01    [Abstracts]
TI: Comparison of Gas Flux and Soil Gas Composition at Two Oil Fields: Rangely, Colorado With CO$_{2}$-EOR, and Teapot Dome, Wyoming at Baseline Condition
AU: * Klusman, R W
EM: rklusman@mines.edu
AF: Colorado School of Mines, Dept. of Chemistry and Geochemistry, Golden, CO 80401 United States
AB: Carbon Dioxide sequestration in spent oil and gas fields will likely be a significant early option that has economic advantages. A concern is the potential for gas microseepage under the overpressured conditions necessary for operation. A comparison was made between the overpressured Rangely, Colorado CO$_{2}$-EOR operation and the underpressured Teapot Dome oil field in Wyoming, which is proposed for CO$_{2}$ sequestration experimentation. Overpressure is important in driving the migration of relatively inert CH$_{4}$ from the reservoir environment, contrasting with more water soluble and reactive CO$_{2}$. Fluxes of CO$_{2}$ into the atmosphere under winter conditions of low soil biological activity averaged 302 and 228 mg m$^{2}$day$^{-1}$, with standard deviations of 1134 and 187 mg m$^{2}$day$^{-1}$, respectively, for Rangely and Teapot Dome. Average fluxes of CH$_{4}$ were 25 and 0.14 mg m$^{2}$day$^{-1}$, with standard deviations of 135 and 0.33 mg m$^{2}$day$^{-1}$, respectively for Rangely and Teapot Dome. Shallow soil gas composition exhibited similar large differences for CH$_{4}$. Median values were more similar at the two fields, reflecting high rates of microseepage at a few locations of those sampled. Stable carbon isotope measurements aided in the recognition of anomalous areas. Ten-meter deep holes were augured for nested soil gas sampling at selected locations of interest for more thorough characterization. Both areas of gas microseepage and background were investigated. In anomalous locations, a substantial proportion of deep-sourced CH$_{4}$ was bacterially oxidized in the unsaturated zone, producing isotopically distinctive and radiocarbon-depleted CO$_{2}$. Carbon isotopic composition of surface materials, such as calcite, caliche, vegetation, soil organic and inorganic matter are essential in the characterization of processes operating in the near-surface.
DE: 1045 Low-temperature geochemistry
DE: 1094 Instruments and techniques
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting