Petroleum geochemistry of San Juan sag, Colorado

Conference · Fri Sep 01 04:00:00 EDT 1989 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5698119

Clayton, J L; Gries, R R ^[1]

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1. Geological Survey, Denver, CO (USA)

Recently, oil and gas shows have been reported in Cretaceous and Tertiary rocks of the San Juan sag, and minor oil production has been established from volcanic rocks (Kirby Petroleum 1 Jynnifer well, Sec. 9, TT40N, R5E). Potential source rocks present in the San Juan sag are the upper and lower (including the Niobrara Member) Mancos Shale (Upper Cretaceous). The combined upper and lower Mancos Shale is about 660 m thick and contains between about 0.5 and 5.5% organic carbon, although most values are between about 1.5 and 2.0%. The Niobrara Member of the lower Mancos Shale has the highest overall organic matter content in the section (organic carbon averages > 2.0%). Pyrolysis and solvent extraction yields (typically 2,000-6,000 and 1,000-4,000 ppm, respectively) indicate that the upper and lower Mancos Shale and the Niobrara Member are all good potential source rocks for oil and gas. Oil-source rock correlations using gas chromatography, mass spectrometry, and stable carbon isotope ratios indicate that the upper Mancos Shale is the most likely source for the oil produced from the 1 Jynnifer discovery well. The source of the oil produced from the nearby Gramps field is less certain but may be the lower Mancos Shale or Niobrara Member. The hydrocarbon generation history of the San Juan sag is complex because of highly variable heat flow in the area caused by Oligocene volcanism. Sills have caused thermal alteration of organic matter in shales on a local scale, and larger volcanic bodies may have produced proportionally larger thermal effects. Localized heating may have caused thermal decomposition of carbonate minerals and generation of high CO{sub 2} gas deposits. Higher regional heat flow associated with volcanism was important in the source rock maturation of this area and maturation was relatively recent (Oligocene to present).

• OSTI ID: 5698119
• Report Number(s): CONF-8910195--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 73:9
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
CENOZOIC ERA
CHEMISTRY
COLORADO
CRETACEOUS PERIOD
FEDERAL REGION VIII
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
MATURATION
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
ORIGIN
PETROLEUM DEPOSITS
RESOURCES
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SHALES
SOURCE ROCKS
TERTIARY PERIOD
USA