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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Advances in Hydrographic Systems Aid Hydrocarbon
Exploration and Geohazard Evaluation
By
AOA Geophysics Inc.
In this presentation, we will discuss the application of hydrographic techniques to both exploration and geohazards.
Exploration
In exploration, a hydrographic
survey can be the foundation of a
two-stage field program whose
objective is to reduce exploration
risk or rank prospect areas, typically
in a block with little previous
exploration and no known discoveries. We typically begin with
an analysis of satellite-derived synthetic aperture
radar (SAR)
images, which can image sea surface slicks. Slicks may provide an
indication of hydrocarbon seepage
to the sea surface, and the
location of the slicks can be tied
to the possible seafloor origination
points of the seeps. Our
approach for the first stage of the
survey is to combine a hull-mounted survey system
(multibeam) with other acquisition
programs that are amenable
to a “mowing the lawn” survey
strategy; this can include the
acquisition of gravity, magnetics and sub-bottom profiler. The
combination of these data sets can define the tectonic fabric
within a block, indicate the presence
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of volcanics or the location of thick basin sequences, image shallow faults and provide an indication of fluids at and immediately below the mud-line.
The process of seepage elevates subsurface geochemical boundaries
that are normally buried to, or near to, the sediment-water
interface. Cores that contain evidence of hydrocarbons may provide
direct samples of the fluids present in a basin without
drilling and may provide information regarding source, maturity,
and degradation. The distribution of seeps on the seafloor may
provide information about the extent of the hydrocarbon system
or information regarding migration
conduits.
Geohazards
For deep water geohazard applications, there have been two trends that have revolutionized deepwater geohazard surveys and interpretations. First, there have been improvements in the acquisition systems themselves, allowing for very high frequency (high resolution) acquisition in water up to 4000m deep. Secondly, there have been dramatic improvements in delivery platforms, including the commercial availability of autonomous underwater vehicles (AUVs) that get the sensors close to the seafloor without the need for a tether for deepwater surveys.
Summary:
Geophysical systems that can be used to evaluate the impedance/ roughness and the shape (bathymetry) of the seafloor, and to identify zones of potential fluid expulsion, range from near-bottom, high frequency (up to 100s of kHz) to regional hydrographic survey systems (10s of Hz), to exploration seismic data (10s to
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