Steve Jones (TCD)

will speak on

Mixing oil and water: The new synergy between reflection seismology and oceanography

Time: 2:15PM
Date: Thu 20th March 2008
Location: Mathematical Sciences Seminar Room [map]

Abstract: When standard seismic reflection processing techniques are targetted at the water layer,
images of oceanic thermohaline structure can result. Hydrocarbon exploration has moved
out into the deep-water frontier over the past two decades, and the expanding database
of seismic reflection profiles across continental slopes and deep water basins now promises
to shed new light on problems such as oceanic mixing and continental slope stability.
Reprocessed legacy seismic data from Rockall Trough, west of Ireland, illustrate several
potential advantages to oceanographers. At the small scale, internal waves of wavelength
several hundred metres to a few kilometres can be observed on single shot gathers, and
their amplitudes, frequencies and propagation speeds measured directly. Maps of internal
wave properties over large spatial areas are beginning to allow wave generation sites
to be identified, so that important generation mechanisms can be inferred. Interesting
features seen on larger scales (tens of kilometres) within the permanent thermocline include
packages of highly reflective water with sharp, very steep boundaries and lenticular
structures that resemble meso-scale eddies. Such features vary on time periods of hours
to days, and the time scales of variation in reflectivity at different spatial scales can be
quantified by looking at overlapping profile segments, intersecting lines within grids of 2D
profiles, and 3D surveys. In future this information might help to estimate mixing rates.
The hydrocarbon industry can also gain from the new synergy. Variations in water-layer
travel time caused by variations in thermohaline structure must be accounted for when
processing 3D and 4D seismic surveys, and it is important to know the strength and variability
of water currents when planning seabed installations. Just as important, there is
‘green capital’ to be made from supplying data for ocean and climate research. In future,
we hope that industry will be able to routinely copy the water-layer part of new seismic
reflection datasets to an international database that can be accessed by ocean and climate
researchers. Such a strategy would benefit society at minimal additional cost to industry.

(This talk is part of the Meteorology series.)

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