Origin of nitrogen-rich natural gases in the California Great Valley: Evidence from helium, carbon and nitrogen isotope ratios

Journal Article · Thu Mar 31 23:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90356-0· OSTI ID:5236468

Jenden, P D; Kaplan, I R ^[1]; Poreda, R J; Craig, H ^[2]

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1. Global Geochemistry Corporation, Canoga Park, CA (USA)
2. Univ. of California, San Diego, La Jolla (USA)

Dry natural gases produced from the Sacramento and northern San Joaquin basins contain up to 87% nitrogen. {delta}{sup 15}N measurements for gases with N{sub 2} {ge} 8% vary from 0.9{per thousand} to 3.5{per thousand}; methane {delta}{sup 13}C values vary from {minus}61{per thousand} to {minus}15{per thousand}. {sup 3}He/{sup 4}He ratios indicate the presence of mantle-derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components: a hydrocarbon-rich gas with {sup 3}He/{sup 4}He {le} 0.1R{sub A} derived from the microbial and thermogenic alteration of sedimentary organic matter, a hydrocarbon-rich gas with {sup 3}He/{sup 4}He {ge} 2.75R{sub A} derived from the localized pyrolysis of sediments by magmatic volatiles, and a nitrogen-rich gas with {sup 3}He/{sup 4}He {approximately} 1R{sub A}. The nitrogen-rich component is characterized by methane {delta}{sup 13}C less negative than {minus}25{per thousand} and N{sub 2}/Ar ratios as high as 22,000. Nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen-rich component is derived from metasedimentary rocks deep within the crust. The Coast Ranges Fraciscan complex, which was thrust well beneath the Great Valley during Late Mesozoic and Early Cenozoic subduction, appears to be the most likely source.

• OSTI ID: 5236468
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:4; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
033000* -- Natural Gas-- Properties & Composition
58 GEOSCIENCES
580000 -- Geosciences
ALKANES
BIODEGRADATION
CALIFORNIA
CARBON
CARBON ISOTOPES
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
EARTH MANTLE
ELEMENTS
ENERGY SOURCES
FEDERAL REGION IX
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOCHEMISTRY
GEOLOGIC STRUCTURES
HELIUM
HELIUM ISOTOPES
HYDROCARBONS
ISOTOPE RATIO
ISOTOPES
METHANE
NATURAL GAS
NITROGEN
NITROGEN ISOTOPES
NONMETALS
NORTH AMERICA
ORGANIC COMPOUNDS
ORIGIN
RARE GASES
SEDIMENTARY BASINS
USA