Print this pageEGLAND, ERIC T., and JORDAN F. CLARK., Department of Geological Sciences, University of California, Santa Barbara; LIBE WASHBURN, Department of Geography, University of California, Santa Barbara; DEREK C. QUIGLEY, Geko-Prackla, Houston, TX; J. SCOTT HORNAFIUS, Mobil Oil Company, Clements Inn, London, UK; and BRUCE P. LUYENDYK, R. DAN FRANCIS, Department of Geological Sciences, California State University Long Beach
Abstract: Comparison of Methods to Determine Gaseous Emissions to the Atmosphere Above Natural Marine Hydrocarbon Seeps
Emissions to the atmosphere from natural marine hydrocarbon seeps offshore
of Coal Oil Point, Santa Barbara Channel, California have been shown to
be a significant source of reactive organic gasses which contribute to
the formation of tropospheric ozone. Three methods were employed to estimate
emission rates: sonar surveys, atmospheric tracer experiments and automated
direct capture experiments. Experiments were conducted over an area of
the La Goleta seeps along the South Ellwood anticline approximately 3 kilometers
offshore from Coal Oil Point. An August 1996 calibrated 3.5 kHz sonar survey
was used to estimate gas seepage emissions of 1.7 x 104 [m3(gas)/day].
Atmospheric tracer experiments sampled the SF6 and source gas mixture downwind
from the source area. Analysis of the methane component of the seep gas
along with SF6 concentrations yielded a CH4/SF6 mixing ratio from which
a seep gas emission estimate was calculated from the known release rate
of the tracer gas. A buoy equipped with a gas capture device directly measured
gas flux at the sea surface. Gas flux estimates from the ongoing sonar
surveys and preliminary results from the atmospheric tracer and direct
capture methods show reasonable agreement in the estimation of the offshore
gas emission rates to the atmosphere.
AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California