Estimated diffusion rates of inorganic gases from southeastern Colorado reservoirs
- Colorado School of Mines, Golden, CO (United States)
Helium, argon, and nitrogen are small, chemically unreactive molecules with relatively large effective diffusion coefficients compared to most hydrocarbons. If these gases have existed in gas fields for even the shortest geologic time spans, steady-state diffusion must be at least approximated, and the diffusional flux of these gases through a reservoir cap rock may be estimated using Fick's First Law of Diffusion. Diffusional loss represents a minimum loss rate since mass transfer along fractures and faults would be faster. Under a steady-state condition, the rate of diffusional loss most be balanced by an equal influx of the gas into the reservoir. Using a natural gas field's estimated reserves, natural gas composition, area, and the estimated flux of a given gas through the field's cap rock, the turnover time of the gas is estimated. Southeastern Colorado gas fields producing from the Morrow Formation often contain anomalously high concentrations of nitrogen (to 70%), helium (to 5%) and yield turnover times for these gases of generally less than 100,000 years. Unless the N{sub 2}, He, and Ar were emplaced within the last 100,000 years, there must be a continuing large flux of gas into these fields to balance the diffusional loss. The large fluxes of inorganic gases required to maintain their concentrations in natural gases raises questions about the age and longevity of gas fields. Extension of these calculations to light hydrocarbons implies that catagenesis is a more recent and ongoing process than is often believed.
- OSTI ID:
- 5846288
- Report Number(s):
- CONF-9109239--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 75:8; ISSN AABUD; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
033000* -- Natural Gas-- Properties & Composition
ARGON
CATAGENESIS
CHEMICAL COMPOSITION
COLORADO
DEVELOPED COUNTRIES
DIFFUSION
ELEMENTS
ENERGY SOURCES
FEDERAL REGION VIII
FICK LAWS
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC DEPOSITS
HELIUM
MINERAL RESOURCES
NATURAL GAS
NATURAL GAS DEPOSITS
NITROGEN
NONMETALS
NORTH AMERICA
RARE GASES
RESERVOIR ROCK
RESOURCES
STEADY-STATE CONDITIONS
USA