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

Journal Article · Fri Apr 01 00:00:00 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]

---

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), Vol. 52:4; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

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