Fugro and AOA Geophysics’ new seafloor map of offshore NE Spain shows unprecedented detail
Posted: 10 September 2004
Fugro Survey Ltd. and AOA Geophysics Inc. have mapped the Cap de Creus canyon head, northeast of Barcelona in the Gulf of Lion, acquiring a data set that demonstrates Fugro and AOA’s extensive capabilities with a hull-mounted multibeam system. The map data, acquired in early July this year, clearly shows a wide range of active geologic processes, from mass wasting and furrows, to faults and seafloor seepage, in unprecedented detail.
The Cap de Creus canyon head, a key feature in the Gulf of Lion, is the subject of an ongoing EuroSTRATAFORM study supported by the European Community and the U.S. Office of Naval Research. EuroSTRATAFORM scientists are already using the Cap de Creus data to plan the acquisition of additional geophysical data, box and piston cores, as well as mooring / oceanographic information for a cruise in September, 2004.
Dr. Tom Drake, team leader for the Office of Naval Research's Coastal Geosciences Program, said, "I am more than pleased with the preliminary data I've seen so far and totally amazed that you were able to get all the necessary logistics lined up in a very short time. Nothing beats real professionals for getting the job done."
The data were acquired with a hull-mounted Simrad 30 kHz EM300 system (1x1 degree configuration) on Fugro's Geo Prospector. Northwest-southeast lines were run approximately parallel to the canyon axis, at speeds varying from 6.5 to 8 knots. The beam configuration was controlled to insure a high ping density at all water depths.
The resultant shaded relief bathymetry has been created with a grid spacing of 10m. No interpolation or smoothing has been applied to the data. In the shallower water portions of the field area (<150m), the grid spacing is 5m. The furrows in the east-central part of the field area are 20-50cm deep, and 20-50m apart. These features are smaller than the advertised accuracy of the system, and attest to our ability to image geologically relevant features with bin sizes significantly smaller than the footprint of individual beams.
Backscatter data show significant variations throughout the field area. Sub-sampled backscatter mosaics of the field area have a pixel size of 1m for all water depths. Backscatter variations appear to be related to changes in seafloor sediment type (hemipelagic drape vs. mass gravity flow / turbidity currents). Really restricted high backscatter zones are related to seafloor outcrops of over consolidated sediment as well as to possible gas seeps (carbonate mounds).
Sub-bottom profiler (pinger) data were acquired with a hull-mounted GeoAcoustics 4x4 transducer array and a Knudsen 320 topside unit. Sub-bottom data were acquired concurrently with multibeam data, at multibeam acquisition speeds. Sub-bottom data show penetrations of up to 40-50m, and clearly image canyon cut-and-fill sequences, folded strata, and geologically recent faulting. Sub-bottom data show the location and distribution of acoustic turbidity in the shallow section, interpreted to be related to shallow gas.
Fugro and AOA have, together and separately, been involved in a number of proprietary survey programs for the oil industry, acquiring multibeam and sub-bottom data concurrently with exploration 2D seismic (4.5 km streamer, 1700 cubic inch gun array), gravity and magnetics data, identifying seafloor features relevant to the hydrocarbon system. Cores have been placed on these features with great accuracy using USBL navigation, yielding data on the presence, distribution, and composition of hydrocarbons in frontier basins.
If 2D seismic data are acquired along with multibeam, Fugro and AOA are able to survey 250 square kilometers per day, or 100 line km of seismic. If 2D data are not acquired, Fugro and AOA are able to survey more than 800 square km per day. On these surveys, Fugro and AOA have achieved data with a bathymetric bin size of 25m in up to 3000m of water, with a backscatter pixel of 5m.
For more information see www.fugro.com
Posted by Richard Price,
Editor Pipeline Magazine
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