Download Geology and Hydrocarbon Potential of the Northern Dreki Area

Geology and Hydrocarbon Potential of the Northern Dreki Area,
Icelandic Continental Shelf
Ministry of Industry
Prepared by Iceland GeoSurvey
January 2008
National Energy Authority
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Three areas on the Icelandic continental shelf are thought to have potential for commercial accumulations of oil and gas. They are Bergrisi in the Hatton-Rockall area, Gammur
on the northern insular shelf of Iceland, and Dreki east and northeast of Iceland. The Icelandic government has announced that it aims to offer exclusive exploration and
production licences in the northern part of the Dreki area. A preliminary date for the start of the licensing round has been set for 15 January 2009.
Figure 1. Three areas on the Icelandic continental shelf with potential for commercial accumulations of oil and gas (purple): Bergrisi,
Gammur and Dreki. A concession round is being prepared for the Northern Dreki Area (red). The area includes the Icelandic part of a joint
development area defined in a 1981 continental shelf agreement between Iceland and Norway (orange).
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The Jan Mayen Ridge, including the part covered by the northern Dreki area, is thought to have potential for hydrocarbon accumulations because of its geological similarity to
hydrocarbon basins which were its next door neighbours prior to the opening of the northeast Atlantic ocean basin. The basins in question are the Jameson Land Basin onshore
East Greenland, where oil is known to have been generated and preserved in sandstone bodies, and basins offshore western Norway, Shetland and in the North Sea , where oil
and gas has been discovered in commercial quantities.
Figure 2. The northern Dreki area and hydrocarbon basins in East Greenland, the North Sea and offshore western Norway and Shetland.
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Prior to the onset of seafloor spreading in the northeast Atlantic 55 million years ago, the hydrocarbon basins shown in Figure 2 were located in close proximity to one another.
Since that time they have gradually moved apart as a result of the plate tectonic movements that created Iceland and the surrounding ocean basins. A part of this development
was that the Jan Mayen Ridge was gradually separated from the continental shelf of Norway and Greenland and became isolated far from shore and surrounded by newly
created ocean floor. This occured in parallel with the gradual emergence of Iceland and its surrounding insular shelf.
Figure 3. The Jan Mayen Ridge (light brown) was separated from the continental shelves of Greenland and Norway by plate
tectonic movements and creation of new ocean floor (blue) concurrently with the gradual emergence of Iceland.
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The northern Dreki area is located on the northeastern continental shelf of Iceland. It includes the Icelandic part of the Jan Mayen Agreement area which was defined in an
agreement reached with Norway in 1981 and straddles the delimitation line between the economic zones of Iceland and Jan Mayen. According to the agreement either
country is entitled to a minimum of 75% of any oil or gas resources within its own part of the agreement area as well as a stake of up to 25% in any hydrocarbon activities in
the other country's part of the area.
Figure 4. Location of the northern Dreki area on the northeastern Iceland shelf. The Jan Mayen Agreement area straddling the
delimitation line between the economic zones of Iceland and Jan Mayen (Norway) shown for comparison. Limits of the Exclusive
Economic Zones of Iceland, Jan Mayen, Greenland and the Faroe Islands shown in black.
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The generation and accumulation of oil and gas is dependent on many factors. For this to happen certain conditions must be present and certain events must happen in a
particular order. Broadly speaking the chain of events is the following: Organic remains settle on the seafloor together with other sediment under oxygen-deficient conditions
which prevent the remains from being consumed by bottom-feeding organisms. They are then buried by younger sediments and gradually compressed into a source rock and
heated as a result of the general increase of temperature with depth below the sea floor. Eventually they start to give off hydrocarbons (oil at first and then gas) which
migrate upwards through the water-filled pores and cracks of the overlying rocks. On their way up the hydrocarbons encounter an impermeable layer (seal or caprock, such as
shale,) and are deflected laterally by it into a local high where they are trapped. If a porous and permeable reservoir rock, such as sandstone, is present below the caprock,
large amounts of oil and gas may accumulate within the trap over time.
Figure 5. Generation and accumulation of oil.
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When exploring for oil, the usual procedure is to investigate likely areas in detail with geophysical measurements from the surface before any exploration wells are drilled. The
reason for this is that drilling exploration wells is very costly but the the chances of success can be improved significantly by carrying out geophysical surveys costing only a
tenth of what it costs to drill a well. However, only in exceptional cases do such measurements reveal any direct signs of oil or gas and even when seen such signs are never
unequivocal but only indicators that may have other explanations. A more indirect prospecting method is therefore usually employed in the search for hydrocarbons in which
potential traps are identified on the basis of shape and an assessment is made of whether other geological conditions and steps in the history of development are likely to
have led to the generation of oil or gas and accumulation in the traps. The method is based largely on the interpretation seismic reflection profiles which are of cross-sectional
sonic images of the subsurface strata constructed from reflected sound pulses.
Figure 6. Seismic reflection profile through a possbile hydrocarbon trap in the northern Dreki area.
Bright reflections may be interpreted as indicating the presence of gas?
Exploration of this kind has been carried out in the northern Dreki area in two main phases (Figure 7):
Seismic reflection mapping of the Jan Mayen Agreement area was carried out jointly by Icelandic and Norwegian authorities in 1985 and 1988. Such a mapping
programme was stipulated in the Jan Mayen Agreement.
Seismic reflection mapping of the northern Dreki area was carried out for commercial purposes by Wavefield Inseis in 2001 under the first prospecting licence
awarded in accordance with the Hydrocarbon Act of 2001.
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Figure 7. Bathymetric map of the northern Dreki area. Water depths in the area mostly range from 1500 to 2000 m.
Limits of the Jan Mayen Agremeent area and the Exclusive Economic Zones of Iceland and Norway shown for comparison.
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Seismic reflection
surveys in
the Jan Mayen
Area
Joint IcelandicNorwegian
surveys in
1985 and 1988
Wavefield Inseis
2001 survey
Iceland GeoSurvey2008
Figure 8. Location of seismic reflection profiles acquired jointly by the National Energy Authority of Iceland
and he Norwegian Petroleum Directorate in 1985 and 1988 and by Wavefield Inseis in 2001.
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Figure 9. Simplified geological map of the Jan Mayen Ridge. Line AB shows location of cross-section in Figure 10.
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Figure 10. Simplified cross-section of the Jan Mayen Ridge. Location shown in Figure 9.
The Jan Mayen Ridge is a sliver of continental crust – a microcontinent – bounded by rifted continental margins on both sides. The eastern margin developed as the outermost
part of the continental shelf of Greenland during the initial breakup of the continent and the opening of the Norway Basin. It is characterized by an eastward thickening pile of
basaltic lava flows which was erupted over the pre-existing continent during the events leading to the creation of the ocean basin east of the ridge (Norway Basin). The western
margin developed as a result of rifting within the Greenland continental shelf and seafloor spreading on the Iceland Plateau. It is characterized by tilted extensional fault blocks
and an extensive complex of sills or lava flows which covers the deep basins west of the ridge.
Main geological units in order of age:
1) Continental basement rocks (Basement).
2) Sedimentary rocks pre-dating the opening og the Norwegian-Greenland Sea (light brown).
3) Subaerial basaltic lavas extruded during initial breakup of the continent (purple).
4) Oceanic crust in the Norway Basin (light blue, eastern end).
5) Sedimentary rocks derived from Greenland and deposited prior to the onset of rifting within the Greenland shelf (light red).
6) Sedimentary rocks deposited during rifting within the Greenland shelf (blue).
7) Lava flows or a complex of flat-lying intrusives emplaced just prior to breakup within the Greenland shelf (green).
8) Oceanic crust on the Iceland Plateau (light blue, western end).
9) Sediments deposited after breakup west of the ridge during seafloor spreading on the Iceland Plateau (light brown).
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Figure 11. Igneous features at the easterm margin of the Jan Mayen Ridge and their stratigraphic relationship to sedimentary layers.
An extensive complex of igneous rocks is present along the eastern margin. The volcanic rocks overlie continental pre-opening rocks as a thin layer which thickens towards the
continent-ocean boundary and merges with oceanic crust in the Norway Basin. The main geological units are:
1) A sequence of seward dipping reflectors interpreted as a pile of subaerial basaltic lava flows. The pile forms juxtaposed and partly overlapping wedge-shaped units, the
inner and the outer wedge.
2) Complex of intrusives. A series of west-dipping reflector segments, interpreted as a dike swarm, crosscuts the stratification of the inner wedge as well as the
underlying continental rocks. A number of short-horizontal reflectors, interpreted as sills, are found within the post-opening sediments.
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Prior to the initial opening of the Norwegian-Greenland Sea 55 million years ago (mya), the Jan Mayen Ridge (JMR) was located in the western part of a regional sedimentary
rift basin between Greenland and Norway. After the opening , the ridge gradually emerged as a separate structural entity. The geological development of the ridge may be
divided into four main phases. (Illustrations modified from source [3]):
1) The eastern margin was formed as the continent broke up on the Greenland side of the regional sedimentary rift basin between Greenland and Norway. Basaltic lava
flows were erupted subaerially over the continent. On the outer margin, which now constitutes the eastern flank of the ridge, they form a wedge-shaped pile
thickening eastwards into the line of breakup. There the pile merges with the oldest oceanic crust in the Norway Basin. Elsewhere on the ridge the lavas are thought
to form a relatively thin layer. Pre-rift sediments are imaged locally beneath the lavas. They are probably analogs to sediments preserved onshore East Greenland but
their distribution is not well known. There is little evidence for rift-related faulting beneath the lava cover, the rifting was apparently concentrated on a few widelyspaced faults.
Figure 12 a. Intitial
breakup of the continent
and eruption of lavas.
2) Breakup was followed by seafloor spreading in the Norway Basin and gradual cooling and subsidence of the eastern margin. Sediments derived from Greenland began
to accumulate at the margin on top of the lavas.
Figure 12 b. Sediment
accumulation on the East
Greenland margin.
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3) The western blockfaulted margin was formed when a new rift opened on the East Greenland margin and began to separate its outermost part from the rest of the
continent in a 25 million year long process that operated contemporaneously with seafloor spreading in the Norway Basin. The rifting process broke the earlier
continental margin into a series of tilted fault blocks which subsided to form a rift graben bounded on the east by the emerging ridge. As the incipient rift subsided,
sediment input from Greenland to the ridge, was shut off. Parts of the ridge were uplifted above sea level and eroded extensively. Shortlived submarine fans
developed on both flanks of the ridge in response to sediment supply from its exposed top.
Figure 12 c. Rifting within
the East Greenland
margin.
As the local provenance areas were submerged some time prior to breakup west of the ridge, the ridge complex became sediment starved. At breakup, the plains west
of the ridge, which lay several hundred meters below sea level, were covered with flatlying basalts. These were either empaced as voluminous submarine lava flows or
as an extensive complex of sills just beneath the seafloor.
Figure 12 d. Breakup to
the west of the ridge and
emplacment of sills or
submarine lavas.
4) After breakup the ridge continued to subside, driven by cooling and thermal contraction. Sedimentation became increasingly pelagic, but due to the steep slopes
created in the second rift phase, some gravity flow of sediments continued onto the basin plains from both the eastern and the western slopes.
Figure 12 e. Present.
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Figure 13. Geological map of the northern part of the Dreki area.
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Figure 14. Geological map of the northern part of the Dreki area. Areas with potential hydrocarbon traps from Sagex 2006.
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Hydrocarbon Potential
Several factors indicate that the northern Dreki area may have significant hydrocarbon potential:
1) Sedimentary rocks of sufficient thickness and age are present.
2) There are indications of the presence of sedimentary strata pre-dating the initial opening of the
Norwegian-Greenland sea . Such sediments are likely to be analogous to those preserved in the
Jameson Land Basin onshore East Greenland where source rocks are present and oil known to have
been generated.
3) Reservoir rocks are also likely to be present. Among the candidates are submarine fans derived from
East Greenland.
4) Structures and stratigraphic configurations with potential to act as hydrocarbon traps are clearly
present.
5) Seismic reflection anomalies are observed which may indicate the presence of hydrocarbons.
The area is, however, in the initial stage of exploration. Sufficient seismic reflection data is available to do
in-depth studies, but no exploration wells have been drilled in the area to date. Calibration of lithology,
physical properties and age is therefore still lacking.
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Main sources
[1] Bott, M.H.P., 1985. Plate tectonic evolution of the Icelandic transverse ridge and adjacent regions, J. Geophys. Res., 90, 9953-9960.
[2] Sagex 2006. Preparations for awarding licenses for exploration and production of hydrocarbons. Basic premises, possible development paths and scenarios. Report
prepared for the Ministry of Industry and Commerce by the Norwegian oil & gas exploration and production consultancy group Sagex AS.
http://www.idnadarraduneyti.is/media/Acrobat/SAGEX_Project_G-1_Report.pdf
[3] Gunnarsson, K., Sand, M. and Gudlaugsson, S.T., 1989. Geology and hydrocarbon potential of the Jan Mayen Ridge. Oljedirektoratet, OD-89-91 and Orkustofnun OS89036/JHD-07, report, 143pp, 5 appendices incl. 9 maps. (restricted)
[4] Åkermoen, T., 1989. Jan Mayen-ryggen: Et seismisk stratigrafisk og strukturelt studium. Cand. scient. thesis, University of Oslo. 183pp, 9 maps. (in Norwegian)
Other useful references
Gudlaugsson, S.T., Gunnarsson, K., Sand, M. & J. Skogseid, 1988. Tectonic and volcanic events at the Jan Mayen Ridge microcontinent. In Morton, A.C. & Parson, L.M. (eds.),
1988, Early Tertiary volcanism and the opening of the NE Atlantic, Geological Society Special Publication No. 39, pp. 85-93.
Johansen, J.-M., 1992. Modellering av det magnetiske anomalifeltet over Jan Mayen-ryggen. Cand. scient. thesis, University of Oslo, 111 pp. (in Norwegian)
Kodaira, S., Mjelde, R., Gunnarsson, K., Shiobara, H. & Shimamura, H., 1998. Structure of the Jan Mayen microcontinent and implications for its evolution. Geophys. J. Int., 132,
383-400.
Kuvaas, B. & Kodaira, S., 1997. The formation of the Jan Mayen microcontinent: the missing piece in the continental puzzle between the Møre-Vøring Basins and East
Greenland. First Break, 239-247.
Ólafsson, I. & Gunnarsson, K., 1989. The Jan Mayen Ridge. Velocity structure from analysis of sonobuoy data. Orkustofnun, Reykjavík, Report OS-89030/JHD-04, 62 pp.
Rudjord, J.E., 1990. Jan Mayen-ryggen – seismiske hastigheter og tyngdemodellering. Cand. scient. thesis, University of Oslo, 119 pp. (in Norwegian)
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