Abiogenic hydrocarbons and mantle helium in oil and gas fields

Journal Article · Fri Jan 01 00:00:00 EST 1993 · United States Geological Survey, Professional Paper; (United States)

OSTI ID:7052010

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

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1. Global Geochemistry Corp., Canoga Park, CA (United States)
2. Univ. of California, San Diego, La Jolla, CA (United States)

Most carbon degassed from Earth's interior is released as volcanic and hydrothermal carbon dioxide along oceanic spreading ridges and as volcanic and geothermal carbon dioxide in continental regions. The chemistry of the earth's interior is poorly understood, however, and methane, rather than carbon dioxide, may be the dominant form of carbon throughout much of the mantle. According to one hypothesis, methane from the mantle is continuously injected into the deep crust at lithospheric plate boundaries, ancient suture zones, and other areas of crustal weakness such as large meteorite impact sites. Where introduced beneath sedimentary basins this methane could accumulate in the conventional structural and stratigraphic traps in which we find petroleum. Geochemical evidence strongly argues that crude oil is of sedimentary (biogenic) origin, but the origins of natural gas are more complex and the proportion that may be derived from mantle (that is, abiogenic) sources is unknown. Using a geometric mean of 3x10[sup 6] for the molar CH[sub 4]/[sup 3]He ratio in uncontaminated, mantle-derived fluids from spreading ridges, mantle plumes and summit fumaroles of arc volcanoes, the median abiogenic methane content of commercial gases is estimated to be less than 200 ppm by volume (range=0 to 12,000 ppm). While admittedly a rough estimate, this calculation suggests that little confidence should be placed in the resource potential of abiogenic natural gas. In rift or convergent margin basins, hot magmatic fluids can strip methane and other volatiles from metamorphic basement and overlying sedimentary rocks, however, and commercial accumulations of this type of gas may be present. The economic value of such reserves could be impaired by dilution with carbon dioxide and possibly nitrogen. 171 refs., 13 figs., 2 tabs.

• OSTI ID: 7052010
• Journal Information: United States Geological Survey, Professional Paper; (United States), Vol. 1570
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
HELIUM
SYNTHESIS
METHANE
ABIOGENIC GAS
CHEMICAL COMPOSITION
EARTH MANTLE
METAMORPHISM
NATURAL GAS FIELDS
OIL FIELDS
TRAPPING
ALKANES
ELEMENTS
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC DEPOSITS
HYDROCARBONS
MINERAL RESOURCES
NATURAL GAS
NATURAL GAS DEPOSITS
NONMETALS
ORGANIC COMPOUNDS
PETROLEUM DEPOSITS
RARE GASES
RESOURCES
030200* - Natural Gas- Reserves
Geology
& Exploration