Geological mapping

Resrapp2016engelsk-ingress
04.05.2016
Geological mapping by the NPD in unopened and frontier areas of the NCS helps to enhance understanding of the geology and to expand data coverage. Funds for this work are provided over the government budget.

Geophysical surveys

Seismic surveys

Acquisition of seismic sections involves generating sound waves from a source above or in the subsurface. These waves propagate through the strata and are reflected back to sensors on the seabed, at the sea surface or in a well. That makes it possible to form a picture of the sub-surface geology. Seismic mapping of the NCS began in 1962.

  • 2D seismic: Data acquired, processed and presented as separate seismic lines/cross-sections through the sub-surface.
  • 3D seismic: Data acquired as closely packed separate lines, but processed and presented as a three-dimensional volume of the sub-surface.

Gravimetric surveys

 Measuring variations in the Earth’s gravitational field in order to reveal the composition of the sub-surface.

Magnetometric data

Measurements of variations in the Earth’s magnetic field in order to reveal the composition of the subsurface.

Shallow boreholes

Holes drilled in order to acquire information on the rock characteristics and/or carry out geotechnical examinations for the location of installations and which are not drilled to discover or delimit a petroleum deposit or to produce or inject petroleum, water or other medium (section 2, resource management regulations). The boreholes are cores drilled to a maximum of 200 metres. The consent of the Petroleum Safety Authority Norway must be secured to go deeper than 200 metres. See section 25 of the management regulations.

Acquisition of geological information by the NPD and its mapping of unopened and frontier parts of the NCS help to increase understanding of the geology in these areas and to expand data coverage. A good data and knowledge base is essential for the government to play a crucial role in resource management. Funding of the NPD’s mapping work is provided over the government budget.

 

Seismic surveys in Barents Sea North and North-East

The NPD acquired a total of 32 600 kilometres of 2D seismic data in Barents Sea North and North-East during 2012-14. These surveys were mainly conducted in the area north of 74° 30’ N, which has not been opened for petroleum activities.

A total of 13 700 kilometres of long lines were systematically acquired during 2012 in a relatively tight mesh over the new area to the east, close to the boundary with the Russian sector. Previous surveys in this area had been limited. Favourable ice conditions also made it possible to acquire three seismic lines right up to 81° N (figure 6.1).

 

Figure 6.1 Seismic surveys in Barents Sea North and North-East.

Figure 6.1 Seismic surveys in Barents Sea North and North-East.

 

Data acquisition in 2013 and 2014 took place mainly in the eastern part of Barents Sea North, again close to the Russian boundary, covering 13 200 and 5 700 kilometres respectively. West of the area where Norway and Russia had overlapping claims, older data are available from 1971-97. Their quality is mostly poor, and they were acquired with older technology. Conducting new surveys has accordingly been important in obtaining a better geological understanding of the area.

Gravimetric and magnetometric data were also acquired at the same time as the seismic surveys in 2012-14. This information will help to increase understanding of the geology in the area.

All the seismic data acquired in 2012-14 have been processed. Hard and uneven seabed conditions as well as shallow water made this work very demanding. That applies particularly to the areas around Bjørnøya and up towards Svalbard. As a result, the data are currently being reprocessed (2014-16).

 

Shallow boreholes in Barents Sea North

Geological mapping in Barents Sea North began with 2D seismic surveys in the mid-1970s. Acquiring geological cores eventually became necessary in order to understand which rocks were producing the seismic signals (reflectors) visible in the data. Learning about the age of the rocks was also important in order to understand the geological development of Barents Sea North over time. Several shallow scientific boreholes were drilled in the late 1980s to increase geological knowledge of the area. The last of these surveys was conducted east of Kong Karls Land in 2005.

In the years following the 2011 ratification of the boundary treaty with Russia, the NPD received funds over the government budget for 2D seismic surveying in the new areas. Knowledge of the rocks there is limited, particularly in the northern part. Acquiring new cores is therefore crucial for mapping the far north along the boundary with Russia.

Funds were appropriated in the 2015 government budget for shallow drilling, and cores up to 200 metres long were collected. The primary area for this work lay south and north of Kvitøya (figure 6.2). Outcropping rocks of various ages are found at the seabed there, with the Triassic series and contact with the underlying Permian of great geological interest (figure 6.3). The water depth is 230-360 metres.

 

Figure 6.2 Shallow boreholes in Barents Sea North.

Figure 6.2 Shallow boreholes in Barents Sea North.

 

 

Figure 6.3 Seismic cross-section showing boundaries of rock outcrops.

Figure 6.3 Seismic cross-section showing boundaries of rock outcrops.

 

Seven successful shallow boreholes were drilled with depths varying from 52 to 200 metres. Locations were chosen on the basis of 2D seismic data, and the objective was to retrieve cores from stratigraphic boundaries which primarily occur at deep levels in the Barents Sea but which, for various reasons, are found at shallow depths in the survey area. A total of 1 048 metres of cores were retrieved, and knowledge acquired from these will increase geological understanding of the northern Barents Sea.

Preliminary results from the shallow drilling south of Kvitøya show that the oldest rocks are from the Carboniferous and Permian, with deposition of carbonates and shales. The Permian-Triassic boundary is well preserved in the cores. A dark shale from the Middle Triassic found in the cores is expected to be rich in organic material. A borehole drilled north of Kvitøya has revealed dolomites which were probably deposited in the Carboniferous.

Very thick sandstone layers with thin coal beds have been deposited in the Late Triassic. A preliminary interpretation is that these strata were deposited as a big river plain at the northernmost edge of the Barents Sea. This plain was flooded by the sea, with deposition of marine shales, before a new pulse of sandstones was deposited at the Triassic-Jurassic boundary. More exact dating of the material in the cores and studying the chemical properties of the rocks will provide important information for further geological interpretation of the area.

 

Expedition with ROV

An expedition with a remotely operated vehicle (ROV) was undertaken in 2013 by the NPD in cooperation with the University of Bergen. Covering the north-western part of the Norwegian Sea in just under 3 500 metres of water, it aimed to acquire rock samples from beneath the volcanic basalt in a cost-effective manner. This was done by installing a chain saw in order to cut samples from steep rock outcrops. Locations were determined using seismic and bathymetric information. The material recovered from the southern end of the Gjallar Ridge (figures 6.4, 6.5 and 6.6) reveals the presence of a number of thick intrusions which have solidified as columns. Uranium/lead (U/Pb) dating gives their age as Late Palaeocene (57 million years ago), and they have intruded into fine-grained Upper Cretaceous (Maastrichtian and Campanian) sediments. No sedimentary rocks older than Late Cretaceous were encountered, which accords with the results from the 6603/5-1 (Dalsnuten) exploration well.

Geological samples were also retrieved on the same expedition from the Vøring Spur (figures 6.4, 6.7 and 6.8). Upper Cretaceous volcanic rocks and fine-grained sediments were encountered here. Manganese deposits were also identified in this area.

 

Figure 6.4 Areas explored by ROV in 2013.

Figure 6.4 Areas explored by ROV in 2013.

 

Figure 6.5 Seismic lines illustrating ROV dives on the southern extension of the Gjallar Ridge.

Figure 6.5 Seismic lines illustrating ROV dives on the southern extension of the Gjallar Ridge.

 

Figure 6.6 The Gjallar Ridge, with sampling points and 100-metre contours for water depth.

Figure 6.6 The Gjallar Ridge, with sampling points and 100-metre contours for water depth.

 

Figure 6.7 Seismic lines showing ROV dives on the Vøring Spur.

Figure 6.7 Seismic lines showing ROV dives on the Vøring Spur.

 

Figure 6.8 The Vøring Spur, with sampling points and 100-metre contours for water depth.

Figure 6.8 The Vøring Spur, with sampling points and 100-metre contours for water depth.

 

Shallow boreholes in the western Møre Basin

Few data have been acquired earlier in the western part of the Møre Basin. To increase understanding of the geology, shallow boreholes were drilled on the Møre Marginal High in 2014, 40 kilometres north-west of well 6403/6-1 (Edvarda) (figure 6.4).

The water depth in the area surveyed is about 2 100 metres, and drilling was limited to 200 metres beneath the seabed. The primary objective of the expedition was to recover cores from tilted reflectors deeper than 130 metres beneath the seabed in order to clarify whether these are sedimentary and/ or volcanic rocks (figure 6.9). The results show that these tilted reflectors comprise volcanic rocks formed by rapid cooling of lava coming into contact with seawater. That provides important information on the geological development of this part of the Norwegian Sea. The drilling yielded no information about possible exploration targets beneath the basalt.

 

Figure 6.9 Seismic cross-section showing tilted reflectors from depths of 130 to 170 metres.

Figure 6.9 Seismic cross-section showing tilted reflectors from depths of 130 to 170 metres.

 

New structural elements in Barents Sea South-East

New structural elements in Barents Sea South-East Mapping of Barents Sea South-East by the NPD has identified a number of large geological structures in this area. Four new structural elements have so far been defined and formally approved by the Norwegian Committee on Stratigraphy (Mattingsdal et al, 2015). These structures have been named after vessels used for research in Arctic waters.

Haapet Dome: Haapet was the sailing ship used by geologist Balthazar Mathias Keilhau for what has been described as the first proper scientific expedition to Svalbard in 1827. The structure is a large low-relief dome with a diameter of roughly 40 kilometres.

Veslekari Dome: Veslekari, built in 1918, was the third ultra-robust wooden ship built for Arctic conditions after Fram and Maud, and carried a number of scientific expeditions in high latitudes. The structure is a large elliptical dome, about 50 kilometres long by 25 wide.

Signalhorn Dome: Signalhorn, built in 1914, was an Arctic vessel used for both scientific expeditions in these waters and oil exploration around Svalbard. The structure is a large, oblong, low-relief dome, about 60 kilometres long by 15 wide.

Polstjerna Fault Complex: Polstjerna, build in 1949, was used in part for scientific expeditions around Svalbard and ranks today as Norway’s best-preserved Arctic vessel. It is on display at Tromsø Museum. The structural element represents a fault zone separating the Bjarmeland Platform from the northernmost part of the North Cape Basin.

Reference:
Mattingsdal, R, Høy, T, Simonstad, E, and Brekke, H, 2015, An updated map of structural elements in the southern Barents Sea. Poster presented at the 31st Geological Winter Meeting, 12-14 January 2015, Stavanger.