Evidence of shallow hydrocarbons offshore northern Santa Cruz county, California

Journal Article · Sun Aug 01 04:00:00 EDT 1982 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6646816

Mullins, H T; Nagel, D K

Analyses of high-resolution seismic reflection profiles and hydrocarbon samples indicate that natural hydrocarbon seepage is occurring along the San Gregorio and Monterey Bay fault zones offshore northern Santa Cruz County, California. A variety of anomalous seismic reflection features such as a water-column anomalies, subsurface amplitude anomalies (''bright spots''), and seismic ''smears/wipeouts'' has been observed and mapped. More than 100 water-column anomalies (probably gas seeps) occur in the study area of approximately 270 mi/sup 2/ (700 km/sup 2/). Many of these seismic anomalies are associated with subsurface geologic structures, which suggest hydrocarbon migration from depth. Samples of natural gas collected from a shallow coastal water well contain 74 to 91% methane, 7 to 23% nitrogen, approx.2% carbon dioxide, and < 1% ethane. The methane appears to be thermogenic in origin, having delta/sup 13/C values of -29.51 to -32.55% PDB. Rock dredges from 2,300 ft (700 m) of water in Ascension Submarine Canyon have also recovered oil-saturated sandstones, further suggesting the seepage of hydrocarbons. The shallow occurrence of most of these hydrocarbons are interpreted to be the result of migration from depth along active faults within the San Gregorio and Monterey Bay faults zones.

• Research Organization: Moss Landing Marine Laboratories, CA
• OSTI ID: 6646816
• Journal Information: Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 66:8; ISSN AAPGB
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
&amp; Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
&amp; Exploration
ALKANES
CALIFORNIA
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
ELEMENTS
ENERGY SOURCES
ETHANE
FEDERAL REGION IX
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC DEPOSITS
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
HYDROCARBONS
METHANE
MIGRATION
MINERAL RESOURCES
NATURAL GAS
NATURAL GAS DEPOSITS
NITROGEN
NONMETALS
NORTH AMERICA
OFFSHORE SITES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PETROLEUM DEPOSITS
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEISMIC SURVEYS
SURVEYS
USA