Seafloor Raster Maps and Exploration Metadata

About Datasets in the Icelandic Continental Shelf Portal

Seafloor Raster Maps

In geophysical exploration, various methods are used to measure the physical properties and anomalies of the subsurface. The measurements are used to detect or indicate the presence of hydrocarbons, geothermal reservoirs, groundwater reservoirs and other geological structures. Exploration methods are e.g. seismic reflection and refraction, gravitational and magnetic measurements. When exploring the seafloor, seismic reflection measurements reveal the layering of the subsurface, while gravitational measurements indicate the density of the crust which can be used to determine if it is continental or oceanic crust. Magnetic measurements reveal the magnetic bearing in the crust, indicating if the crust is of continental or oceanic origin, since oceanic crust takes on the magnetic bearing at the time of formation which can be used to determine the approximate age of the crust.

Magnetics

A magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying material. The magnetic variation in successive bands of ocean floor parallel with mid-ocean ridges is important evidence supporting the theory of seafloor spreading, central to plate tectonics. The Arctic and North Atlantic oceans magnetic anomalies data set in the portal was released by Geological Survey of Canada (GSC) in 1996. The main objective of this project was to combine data sets into a coherent grid, observations made during a period of several decades in different geographic locations and under variable circumstances.

Gravity

The surface of the ocean bulges outward and inward mimicking the topography of the ocean floor. The ruffles, too small to be seen, can be measured by a radar altimeter aboard a satellite. As the spacecraft orbits the earth it collects a continuous profile of geoid height across an ocean basin. Profiles from many satellites, collected over many years, are combined to make high resolution images. Marine gravity anomalies derived from radar altimeter measurements of ocean surface slope are the primary data for investigating global tectonics and continental margin structure. Satellite altimetry has provided the most comprehensive images of the gravity field of the ocean basins with accuracies and resolution approaching typical shipboard gravity data. 

The gravity anomaly data set in the portal was collected by the European Space Agency ERS-1 altimeter and the US Navy Geosat altimeter. Those data have provided detailed measurements of sea surface height over the oceans and a first view of the ocean floor structures in many remote areas of the Earth. All of the major petroleum exploration companies use satellite altimeter gravity data from Geosat and ERS-1 to locate offshore sedimentary basins in remote areas. This information is combined with other reconnaissance survey information to determine where to collect multi-channel seismic survey data.

Bathymetry

The Jan Mayen Ridge is a complex ridge system that stretches south from the fracture zone in the north. While this ridge system is believed to consist primarily of continental crust, there are also some oceanic crust characteristics along its flanks. The Jan Mayen Ridge may roughly be divided into two main sections: the main ridge in the north, and the southern ridges. The main ridge stretches from the fracture zone in the north all the way to the Jan Mayen Trough, which intersects the ridge from southwest to northeast. The northern part is relatively flat and stands somewhat higher than the southern part.

There are three kinds of bathymetric data in the Portal: 1) International bathymetric database (SRTM30plus) that is on the one hand built from depth calculations that are based on gravity surveys from satellites, and on the other hand from bathymetry surveys taken by ships. 2) Digitized bathymetric map from Tor Åkermoen's cand. scient. dissertation at the Geology Department of the University of Oslo, reprinted with his permission. 3) Multibeam bathymetry survey conducted by the Marine Research Institute in June 2008, which covers about one-fourth of the northern Dreki Area. These are the best bathymetric data available for the area.


Exploration Metadata

When exploring for oil and gas, the first stage invariably begins by thoroughly researching the area using geophysical techniques before drilling test wells. Geophysical surveys are much less costly than drilling and can increase the chance of success considerably. Nevertheless, geophysical surveys cannot prove the presence of oil or gas; rather they indicate varying degrees of probabilities. Thus, it is necessary to drill wells in order to confirm the stratigraphy interpreted based on seismic data, and to explore for oil or gas fields. Geophysical surveys are used to make a geological model of the area under investigation, whereby its development is recreated as closely as possible in order to illustrate the processes that could have led to the formation of oil and gas. The most important data for making a model, before the drilling stage begins, are derived from seismic reflection measurements, in addition to bathymetric, gravity and magnetic surveys.  

Satellite Seep Studies

Hydrocarbon oil and gas below the seabed can seep from the sea floor and rise as a plume through the water column, resulting in oil slicks on the sea surface. Detecting and identifying such slicks can guide and focus exploration efforts. For offshore exploration, satellite radar or SAR (Synthetic Aperture Radar) can now offer the oil industry an effective, low-cost technique for reducing source risk in high-cost exploration environments such as the deep frontier basins. This is due to their ability to image surface oil seeps remotely with wide swath coverage.

Synthetic Aperture Radar (SAR) is an active microwave instrument, producing high-resolution imagery of the Earth's surface in all weather. A SAR satellite scan the ocean continuously on fixed polar orbits and creates images of the sea surface detailing its morphology. Radar images maps flat patches of the surface that can be related by analysis to petroleum seepage. SAR seep detection is a proven technique for mapping oil seeps and can provide the first indication of the existence of black oil petroleum systems.  

Surface Samples

As it is expensive to drill wells, it is important to be able to gain information on possible formation of hydrocarbons in deep geological strata with less expensive methods. One way to do that is to collect cores of surface sediments and analyze those with geochemical techniques for traces of thermogenic hydrocarbons. The cores need to be long enough so it is possible to collect a subsample from within the anoxic part of the sediments. However, the depth to the anoxic zone varies depending on local conditions, but it is typically enough to collect cores that are longer than 2 m. Information in this category will, at first, only be on cores that have been collected in the northern part of the Dreki area for geochemical analyses. 

Wells 

A lot of information on the subsurface can be learned from geophysical techniques. However, in order to truly understand the subsurface strata and explore for oil and gas reservoirs it is necessary to drill wells. Offshore wells can be drilled using several different types of facilities depending on local conditions such as water depth. These include drill-ships that are kept in place with a dynamic positioning system and platforms that are anchored to the sea floor. 

So far only shallow wells have been drilled on the Icelandic continental shellf, including the Jan Mayen Ridge area. The wells were drilled by Glomar Challenger during the Deep Sea Drilling Project and JOIDES Resolution during the Ocean Drilling Program. To date only shallow boreholes have been drilled at, and in the vicinity of, the northern part of the Dreki Area.

Seismic Reflection

Seismic reflection measurements are geophysical measurements that can be used to research subsurface strata. Measurements are based on the time it takes for a sound wave to travel the depth of the water, bounce off a subsurface reflector and travel back, which is called two-way time (TWT). When researching the seabed, the ship tows a sound source, i.e. airguns, which are suspended about 10 metres below the sea surface. Towed behind the source is a listening cable several kilometres long comprised of numerous hydrophones. The depth of reflectors can be estimated from TWT and the wave velocity through the subsurface strata, and thus a map of subsurface structures can be made. This category contains information on several surveys that have acquired seismic reflection measurements in the Dreki Area. The oldest data dates from 1978, and the newest from 2008.  

Multibeam Bathrymetry

Seabed mapping is a one of the Icelandic Marine Research Institute´s recent projects which started with the launching of the new research vessel, Árni Fridriksson, in the year 2000. The vessel is equipped with a multibeam echo sounder, which enables detailed mapping of the seabed. Bathymetrical and backscatter data is used to make different kinds of maps, i.e. contour-, sun-illuminated and three-dimensional maps, and maps with information on the substrate.