Complex origin of natural gas in Sacramento basin

Conference · Fri May 01 04:00:00 EDT 1987 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:6252326

Jenden, P D; Kaplan, I R

Models for natural gas geochemistry allow us to distinguish biogenic and thermogenic sources, to estimate source rock maturity, and to evaluate mixing, migration, and possible association of gases with oil or condensate. These simple models appear adequate for old, tectonically stable basins such as the Permian and Anadarko and for younger basins bordering passive continental margins such as the Gulf Coast. However, study of 95 natural gases from the Sacramento basin suggests that the origin of gases in relatively young, tectonically active basins may be much more complicated. The Sacramento basin produces dry gas from Upper Cretaceous-early Tertiary clastic sediments deposited in an active forearc environment. Virtually all fields produce from immature sediments (R/sub 0/ less than or equal to 0.5%) with methane delta/sup 13/C values ranging from -62 to -15 per thousand and C/sub 2/ + concentrations averaging less than 2%. Most of the gas has probably migrated eastward from deeply buried shales and mudstones along the western margin of the basin. However, a few fields contain methane with delta/sup 13/C values suggesting an indigenous biogenic or early thermogenic origin. Calculations indicate that localized pyrolysis of shallow sediments by igneous intrusives could have produced large amounts of methane in the Colusa and Sutter Buttes areas. Gases with heavy methane delta/sup 13/C values (> -25 per thousand) are generally rich in nitrogen (up to 88%) and may be derived from metasedimentary rocks subducted beneath the basin. Complex geological history and multiple hydrocarbon sources combine to make the application of geochemistry a challenge in Sacramento basin exploration.

• Research Organization: Global Geochemistry Corp., Canoga Park, CA
• OSTI ID: 6252326
• Report Number(s): CONF-870606-
• Conference Information: Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Journal Volume: 71:5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CALIFORNIA
CENOZOIC ERA
CHEMISTRY
CRETACEOUS PERIOD
EXPLORATION
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
MATURATION
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NORTH AMERICA
ORIGIN
RESERVOIR ROCK
RESOURCES
SEDIMENTARY BASINS
SOURCE ROCKS
TERTIARY PERIOD
USA