Jan Mayen

02.07.2013

Norway and Iceland reached agreement on 22 October 1981 over the continental shelf boundary between Iceland and Jan Mayen. This agreement called for the establishment of a special collaboration over petroleum activities in a defined part of this area. Covering a total of 45 470 square kilometres, the collaboration area breaks down into 32 750 square kilometres on the Norwegian side of the boundary, and 12 720 square kilometres in the Icelandic sector. See figure 7.1.

Iceland can participate with a 25 per cent share in that part of the collaboration area which lies north of the boundary, while Norway can participate with a corresponding share in that part located south of this line.

The Norwegian government initiated an opening process for petroleum activities in the Norwegian sector of the continental shelf around Jan Mayen in 2010. This process covers an area of about 100 000 square kilometres, bounded by the Greenland continental shelf to the west and the Icelandic continental shelf (ICS) to the south. See figure 7.1. The work includes data acquisition and geological mapping with a view to evaluating the resource potential for petroleum, as well as an environmental impact assessment. These studies will form the decision base for a possible opening.

 

Bilateral boundaries, the collaboration area with Iceland and the area covered by the opening process.

Figure 7.1 Bilateral boundaries, the collaboration area with Iceland and the area covered by the opening process.

 

Iceland carried out its first offshore licensing round in 2009, without awarding any production licences. The country concluded its second round on 4 January 2013 with the award of two licences. Petoro is a participant in both. These licences lie at the northern end of Iceland’s share of the collaboration area, on the boundary with the Norwegian sector.

Pursuant to the 1981 agreement, data have been acquired through a collaboration between Norwegian and Icelandic institutions. Scientific bodies and commercial companies have also collected geological information in the area.

On behalf of the Ministry of Petroleum and Energy, the NPD has mapped the potential for oil and gas resources in the Norwegian sector around Jan Mayen. This work began in 2011, and the first results of the resource mapping were presented in February 2013. However, the NPD’s mapping of the area has not been completed. It will continue to analyse seismic data acquired in 2011 and 2012.

Analysis results from seabed rock sampling conducted in 2012 will also become available in 2013. Furthermore, the Storting has appropriated funds for additional geological mapping around Jan Mayen. Shallow stratigraphic wells are planned by the NPD. The Ministry of Petroleum and Energy has requested an upgraded assessment of the potential for oil and gas on the NCS around Jan Mayen by March 2014.

 

Data

 

Geological data

Three shallow boreholes were drilled in 1974 on the Jan Mayen Ridge as part of the Deep Sea Drilling Project (DSDP). These passed through a shallow unconformity (erosional discordance) into the underlying rocks. See figure 7.2 and figure 7.3.

 

Rocks proven in the boreholes drilled by the Deep Sea Drilling Project in 1974 (Talwani et al, 1976, volume 38). The map shows the location of the two boreholes on a seabed map of the Jan Mayen Ridge.

Figure 7.2 Rocks proven in the boreholes drilled by the Deep Sea Drilling Project in 1974 (Talwani et al, 1976, volume 38). The map shows the location of the two boreholes on a seabed map of the Jan Mayen Ridge.

 

Seismic line NPD-85-32 (reprocessed by Spectrum in 2008-09) showing the location of DSDP 349 (vertical line). The line also shows the regionally widespread unconformity (erosional discordance) between the Upper and Lower Oligocene at a time depth of about 1 500 milliseconds (ms), which corresponds to some 1 150 metres.

Figure 7.3 Seismic line NPD-85-32 (reprocessed by Spectrum in 2008-09) showing the location of DSDP 349 (vertical line). The line also shows the regionally widespread unconformity (erosional discordance) between the Upper and Lower Oligocene at a time depth of about 1 500 milliseconds (ms), which corresponds to some 1 150 metres.

 

The two northernmost locations (346 and 347) were drilled to about 190 metres beneath the seabed, while the southernmost (349) went down to roughly 320 metres. Above the clear unconformity – see figure 7.3 – the boreholes passed through fine-grained sediments deposited at the boundary between the Oligocene and the Pleistocene. See the geological timescale at the end of this report. Fine-grained sediments dated to Late Eocene/ Early Oligocene predominated beneath the unconformity. The location of the boreholes was determined on the basis of seismic data which today look very inadequate. More recent seismic data show that the deepest and best documented borehole (DSDP 349) was drilled in a heavily faulted area beneath the unconformity which is difficult to interpret in detail. The results of the borehole accordingly provide limited information about the rocks.

Geological samples were collected by the NPD in 2011 and 2012 using a remotely operated vehicle (ROV). This work was done in collaboration with the University of Bergen. A gripper arm was used in 2011 to break off rock samples, and a chain saw in 2012 to cut them out. Both sampling campaigns were successful. A number of samples were acquired in both Icelandic and Norwegian sectors. See figure 7.4. Analysis of the 2011 samples has largely been completed, while those from 2012 are being processed. The material has provided important new information about the bedrock on the Jan Mayen Ridge, as illustrated in figure 7.8.

 

Sampling stations for ROV surveys in 2011 and 2012, shown in green and yellow.

Figure 7.4 Sampling stations for ROV surveys in 2011 and 2012, shown in green and yellow.

 

Geophysical data

The NPD first acquired seismic data across the Jan Mayen Ridge in 1979. This was followed up in 1985 and 1988, when seismic surveys were conducted on both sides of the Norwegian-Icelandic boundary in cooperation with the Icelandic authorities. Since then, seismic data have been acquired on the ICS in 2001 and 2008. Nevertheless, the overall coverage was very low – particularly on the Norwegian side. The decision was taken in 2011 to acquire seismic data from the whole area under consideration for opening around Jan Mayen, a total of 15 lines adding up to 3 060 kilometres. Data acquisition was concentrated on the Jan Mayen Ridge south of the island and the neighbouring areas on both sides of the main ridge. See figure 7.5. This was followed up in 2012 with the acquisition of 64 lines totalling 9 508 kilometres.

 

2D seismic data acquired by the NPD in 2011 (red) and 2012 (yellow).

Figure 7.5 2D seismic data acquired by the NPD in 2011 (red) and 2012 (yellow).

 

GeoStreamer technology was used in both 2011 and 2012, with the hydrophone streamer towed at a substantially greater depth than normal. That means the operation can be conducted in poorer weather conditions (higher waves) and thereby becomes more efficient.

Gravimetric and magnetometric data have also been acquired along most of the seismic lines with a view to securing additional information, particularly about the deeper rocks.

Water depth data across central parts of the Jan Mayen Ridge – see the seabed map in figure 7.2 – were acquired in the summer of 2010 in close cooperation with the Icelandic authorities, who have acquired similar data on their side of the boundary. This information is used in the geological mapping as well as in planning locations for ROV sampling and seismic surveys.

Aeromagnetic surveys were conducted over the Jan Mayen Ridge as early as 1976. Such data were later acquired over the eastern part of the ridge in both 2005 and 2011-12. These two data sets have been acquired in collaboration with such bodies as the Norwegian Geological Survey (NGU) and Iceland’s National Energy Authority. Among other contributions, they help to delineate the prospective area south-east of Jan Mayen. Table 7.1 provides an overview of the relevant data for mapping the Jan Mayen Ridge.

 

 

Data  
Shallow boreholes Deep Sea Drilling Project 1974
Bathymetry, multibeam echo sounder Icelandic vessel, Norwegian sector, 2010
2D seismic 1 200 km, NPD, 1979
2D seismic 3 000 km, NPD/Icelandic authorities, 1985
2D seismic 1 500 km, NPD/Icelandic authorities, 1988
2D seismic Commercial surveys, ICS, 2001 and 2008
2D seismic 3 060 km, NPD, 2011
2D seismic 9 508 km, NPD, 2012
ROV, G O Sars Sampling with gripping arm, NPD/University of Bergen, 2011
ROV, G O Sars Sampling with chain saw, NPD/University of Bergen, 2011
Aeromagnetic survey NPD, 1976
Aeromagnetic survey NGU/NPD and others, 2005
Aeromagnetic survey NGU/NPD/Icelandic authorities, 2011-12

Table 7.1 Overview of the most relevant data for mapping the Jan Mayen Ridge.

 

Work on securing the best possible input data for enhancing knowledge of the petroleum geology is still under way. Shallow boreholes are due to be drilled on the Jan Mayen Ridge and the outer parts of the Møre Margin. The intention on the Jan Mayen Ridge is to complement and improve existing information about the Cenozoic rocks. In addition to improved understanding of the local geology, shallow drilling on the Møre Margin will be relevant for understanding Jan Mayen because these two areas were adjacent to each other until the Eocene.

 

Main geological features

Jan Mayen is a volcanic island at the northern end of the Jan Mayen Ridge. Running north-south, the latter is a submarine feature extending about 400 kilometres from Jan Mayen towards the Iceland Plateau. See figure 7.6. At its southern end, the main ridge splits into several smaller ones. Water depths along most of the ridge descend quickly to about 600 metres south of the island, and sink further to roughly 1 000 metres over much of the main ridge. Depths on the Iceland Plateau south and west of Jan Mayen are about 2 000 metres, while they descend eastward towards the Ægir Ridge to a depth of more than 3 500 metres. The ridge is bordered to the north by the Jan Mayen fracture zone, just north of the island, where the water depth drops steeply towards about 2 500 metres.

 

Structural elements in the Jan Mayen area and the assumed extent of the JMM.

Figure 7.6 Structural elements in the Jan Mayen area and the assumed extent of the JMM.

 

The opening of the North Atlantic began 55 million years ago. During the Cenozoic, the Jan Mayen Ridge tore free from both Norway and Greenland and was left out in the ocean as a separate “microcontinent”. This comprises continental rocks similar to those found in eastern Greenland and on the NCS in the Norwegian Sea. See figure 7.7. The Jan Mayen microcontinent (JMM) was formed by an initial separation from the NCS early in the Cenozoic (Early Eocene) as a result of seafloor spreading along the Ægir Ridge, and a subsequent separation from the Greenland continental shelf through seafloor spreading along the Kolbeinsey Ridge.

 

A geological cross-section of the Norwegian Sea from eastern Greenland (EG) in the west, across the JMM, to Norway (MMH).

 

Figure 7.7 A geological cross-section of the Norwegian Sea from eastern Greenland (EG) in the west, across the JMM, to Norway (MMH). The two major continents on either side of the sea are coloured in yellows and browns in the same way as the microcontinent. The grey strata between the continents comprise young seabed crust formed of volcanic rocks without petroleum potential (crustal cross-section taken from Mjelde et al, 2008, Marine Geophysical Researches).

 

The JMM comprises a larger area than the actual Jan Mayen Ridge alone. It is unclear whether it extends beneath Jan Mayen itself, or whether its northern limit runs a little south of the island. The southern boundary is also unclarified. The JMM extends a good way south into the Iceland Plateau and possibly right beneath north-eastern parts of Iceland. Its eastern limit is assumed to lie just east of the boundary of the Jan Mayen Ridge, while its western edge is expected to extend into the Jan Mayen Basin west of the ridge. See figure 7.6.

Rocks and structures in the JMM are little known, particularly at deeper levels. Nevertheless, the location of the microcontinent up to its formation in the Cenozoic conveys information about the rocks likely to be found. During the period from the Caledonian orogeny in the Late Silurian to the start of seafloor spreading in the Early Eocene, the area including the JMM lay between eastern Greenland and Norway. These areas then formed a single continent and experienced the same geological development.

The system of rock layers, unconformities, folds and faults making up the crust of the JMM is more complicated than elsewhere on the NCS. While this is demanding to map and interpret, it provides the key to the understanding of tectonic development and geological history which is necessary for evaluating the resources in the area.

 

Structural geology

Structural geology describes how the Earth’s crust is built up and how that process occurs over time. Known as tectonics, from the Ancient Greek word tektōn or carpenter, this is the science of how the crust has formed. The building materials are the various rocks, assembled in different ways. First and foremost, they are deposited through time as a succession of rock layers (also called a lithostratigraphic sequence). These layers have then been deformed, carved up, trans - ported and reassembled to a greater or lesser extent by crustal forces and movements. How this has occurred in a given location can be traced in part from the way the strata have been folded and offset along faults. Such structures form when the crust is compressed horizontally (strata are folded) or extended (strata are torn apart and displaced along faults). But the crust can also be subject to forces acting vertically, lifting or lowering the rocks over time. When an old succession is elevated above sea level, the rocks will be eroded by wind and weather to create erosional surfaces. Today’s land areas are an erosional surface of this kind. When they then sink below sea level again, they are covered with layers of new sediment which convert into rock in their turn. In that way, the erosional surfaces are preserved in the overall succession as clear breaks or hiatuses in the deposition history, and are termed unconformities or (erosional) discordances.

The main force behind tectonics is the motion over time of the planet’s major crustal plates. Tectonic forces are particularly strong along the boundaries of these plates, whether they are colliding and being squeezed together or moving apart to form new plate boundaries. Moun - tain chains form where two continental plates collide. The Himalayas, for example, are a result of the on-going collision between the Indian and Asian plates. Where a plate is splitting apart, an initial rift valley gradually expands until a new ocean ultimately opens between the two sections of the original continent. The African continent, for example, is breaking apart along east Africa’s Great Rift Valley. The Atlantic Ocean represents the next stage, with the continents on either side of the ocean – which were once joined –being steadily driven further apart. These processes are known as plate tectonics

 

 

The JMM crust is tectonically complicated because it has been at the heart of an area where plate boundaries have developed over geological time. Since the start of the Cambrian about 550 million years ago, the continental margins of eastern Greenland and western Scandinavia have experienced two major plate tectonic events – the continental collision which created the Caledonian mountain chain, and the continental separation with the opening of the North Atlantic. These two incidents divide the tectonic history of the area into three main periods.

  1. Cambrian to Middle Devonian (about 550 to roughly 400 million years ago). As today, Greenland and Scandinavia lay on separate continents on either side of the Iapetus Ocean. During the last half of the period, the two plates began to move towards each other and the intervening ocean steadily closed. Finally, the two landmasses collided and created the Caledonian mountain chain in the process of joining to form a new continent.
  2. Middle Devonian to Eocene (about 400 to roughly 55 million years ago). The area was primarily characterised by crustal extension and rift valley formation. This culminated with the re-separation of the continent between Greenland and Scandinavia at the boundary between the Late Palaeocene and the Early Eocene, which marked the start of today’s North Atlantic.
  3. Early Eocene to the present, comprising the active opening of the North Atlantic through seafloor spreading between Greenland and Scandinavia. At the beginning of this period, today’s JMM was part of Greenland. Later, about 25 million years ago, the JMM separated from Greenland after a period of widespread crustal extension in the area. Since then, seafloor spreading has continued to open the ocean between Greenland and Jan Mayen.

A closer look at the two latest principal periods is relevant for this report.

During the first part of the middle period, from the Middle Devonian to the Eocene, all the continents were assembled into a single large landmass – the supercontinent Pangea (from the Greek word meaning “all earth”). Pangea was formed through a series of plate collisions which raised mountain chains and brought together all the continents during the Devonian, Carboniferous and Permian. Although the supercontinent was primarily experiencing compression as a result of the plate collisions during this period, eastern Greenland and Scandinavia were locally subject to crustal extension. Such extension and rift valley formation occurred in several phases during the Early Carboniferous and at the boundary between the Carboniferous and Permian.

Plate collisions declined around Pangea at the end of the Permian, about 250 million years ago, and the supercontinent began its long global process of breaking up, which is still on-going. Tectonically, the Middle Triassic to the end of the Middle Jurassic was a quiet period throughout the area. The last part of the Middle Jurassic, about 165 million years ago, saw the start of a very active phase with crustal extension across the whole area. This persisted through the Late Jurassic into the Early Cretaceous. During this Kimmeridgian rift phase, a major system of rift valleys formed on the NCS. These were filled with the most important reservoir sandstones and source rocks, deposited from the North Sea to the Barents Sea to form the basis for such fields as Statfjord, Oseberg, Gullfaks, Troll, Heidrun, Åsgard and Snøhvit. That was followed by a phase when areas subject to this crustal extension began to subside because the crust cooled down and became heavier when the extension process had ended.

The areas between Greenland and Norway where the crust was most extended and thinned subsided to become very deep sedimentary basins, which were filled during the Cretaceous with sediments several kilometres thick (including the Møre and Vøring Basins). This subsidence was reinforced by further crustal extension and block faulting, first in a possible phase in the Albian (about 110 million years ago) and then at the boundary of the Turonian and Coniacian (roughly 90 million years ago).

The crustal extension phase ended in the Palaeocene. It was powerful and rapid, and led to the final separation of Norway from Greenland. At the same time, major volcanic eruptions produced enormous volumes of lava at the transition to the Eocene about 55 million years ago. These lava layers in the Jan Mayen area pose a big problem for mapping because they prevent seismic signals penetrating to the underlying sediments. This means in turn that the seismic data do not show strata from the second main period (Middle Devonian to Eocene). In so far as sedimentary successions from this period are present in the JMM, they will have undergone the tectonic development summarised above.

A good picture of the sedimentary successions and tectonic structures in the final main period, above the lava layers, is provided by the seismic data. The JMM appears on the seabed as a narrow uplifted main ridge in the north, which is split up southwards in the Icelandic sector into a number of lower ridges and blocks. The main ridge comprises a steep fault escarpment to the west, a gentler flank to the east and a flat summit. Internally, the ridge is far more complex. To the south, the eastern sections show a relatively simple picture with the sedimentary successions sloping regularly to the east. See figure 7.3. Westwards and northwards under the top of the ridge, the strata are broken up in a complicated fault pattern. These faults are associated with large and small folds. Farthest to the west, everything is truncated by a large fault escarpment.

The flat top of the ridge reflects an erosional discordance which truncates all internal structures. This surface is overlain by a thin sequence of largely flat sedimentary layers (the discordance surface is about 1 500 milliseconds down on the seismic profile in figure 7.3). In the DSDP 349 borehole shown in figure 7.3, the strata below and above this discordance have been dated to the Late Eocene/Early Oligocene and the Late Oligocene respectively. This means that faulting activity and folding, with subsequent uplift and erosion, must have occurred during a relatively short period at the transition to the Late Oligocene. This tectonic activity is attributed to the phase of crustal extension and the final separation of the JMM from Greenland. The process has probably comprised an early phase with substantial extension plus the development of normal faults and large fault blocks, which was replaced by a compression and folding phase.

The flat discordance with the deep erosion of the Jan Mayen Ridge shows that it was substantially uplifted and then eroded down to sea level. This means that the sea level must also have been relatively stable at the transition to the Late Oligocene. The big lower-lying fault blocks in the Icelandic sector to the south have also been uplifted but not eroded. They must have lain beneath sea level throughout or been rapidly inundated. During the Late Oligocene, the Jan Mayen Ridge itself subsided beneath sea level. Since then, the region has been more stable.

 

Rocks

Earlier shallow drilling and sampling in recent years on the Jan Mayen Ridge have secured rock samples from the Triassic, Jurassic, Cretaceous and Cenozoic. Samples collected by an ROV with a chain saw in 2012 (see figure 7.4 and figure 7.8) show that only those from the Cenozoic are definitely indigenous. All the older samples are probably material carried in icebergs from eastern Greenland and dropped over the ridge when the ice melted.

 

Samples acquired by ROV from outcrops on the Icelandic sector of the Jan Mayen Ridge. The column shows rocks which are very probably representative for this part of the ridge complex.

Figure 7.8 Samples acquired by ROV from outcrops on the Icelandic sector of the Jan Mayen Ridge. The column shows rocks which are very probably representative for this part of the ridge complex.

 

The Cenozoic samples confirm thick layers of lava from the continental break-up in the Palaeocene-Eocene. Seismic data show that these layers have a regional distribution and almost certainly belong to the big North Atlantic lava province formed at the time of this continental break-up. In addition, the samples show that the lava layers are overlain by quartz-rich sandstone followed by alternating shales and siltstones. The seismic data also provide details which have been interpreted as possible delta developments of these sediments from west to east, labelled as clinoforms and channel structures in figure 7.9.

 

Interpretation of Eocene delta progradation, with channels and clear clinoforms showing progradation towards the east.

Figure 7.9 Interpretation of Eocene delta progradation, with channels and clear clinoforms showing progradation towards the east.

 

This means that these sediments were deposited at the end of a river system which then drained the inner regions of eastern Greenland, before the JMM split off. These quartz-rich sandstones could be good reservoir rocks. Finegrained material under the quartz-rich sandstone is dated to the Eocene, while the overlying fine-grained sediments have been dated to the Eocene/Early Oligocene. Further up the sedimentary succession, the clear regional discordance lies beneath the Upper Oligocene. The latter probably formed immediately after the crust-extension process which ultimately separated the JMM from eastern Greenland. See figure 7.3. This discordance is not preserved in eastern Greenland, where it would presumably have lain above the level of the Bopladsdalen and Krabbedalen Formations. See figure 7.10.

 

Juxtaposed stratigraphic columns for the continental margins in the Norwegian Sea and eastern Greenland, with the stratigraphy assumed for the JMM.

Figure 7.10 Juxtaposed stratigraphic columns for the continental margins in the Norwegian Sea and eastern Greenland, with the stratigraphy assumed for the JMM.

 

Seismic data show indications here and there of a sedimentary succession under the lava layers, but no reliable rock samples exist from this succession. However, it is likely to resemble the corresponding successions in eastern Greenland and on the NCS in the Norwegian Sea immediately south of the Jan Mayen fracture zone. Before seafloor spreading became established in the Eocene, the JMM formed an area between Kangarlussuaq-Jameson Land in eastern Greenland and the Møre Margin High on the NCS. See figure 7.11.

 

Palaeographic reconstruction of land areas and sediments in the Middle and Late Jurassic for the North Atlantic and Arctic areas

Figure 7.11 Palaeographic reconstruction of land areas and sediments in the Middle and Late Jurassic for the North Atlantic and Arctic areas (Brekke et al, 2001, NPF Special Publication 10). The position of the future JMM is outlined in red.

 

Palaeogeographic comparisons conducted by the NPD and ocean bottom seismic (OBS) surveys show that the pre-Eocene succession is very likely to resemble those on the Trøndelag Platform and Halten Terrace on the NCS and in Jameson Land in eastern Greenland with regard to both rocks and sedimentary thicknesses. See figure 7.10, figure 7.11 and figure 7.12.

 

Crustal model for the JMM based on seismic (refraction) speeds measured with OBS (from Kuvaas and Kodaira, 1997, First Break 15.7).

Figure 7.12 Crustal model for the JMM based on seismic (refraction) speeds measured with OBS (from Kuvaas and Kodaira, 1997, First Break 15.7).

 

During the Carboniferous, the JMM appears to have occupied the watershed between two seas – the Boreal to the north and the Tethys to the south. Carboniferous rocks are accordingly likely to comprise fluvial and lake sediments divided by areas with no deposition.

The Lower Permian is expected to comprise fluvial deposits as a continuation of the Carboniferous. At the boundary with the Late Permian, regional uplift and erosion in Greenland produced a marked erosional discordance. The sea level then rose and transgressed from the north, so that the Upper Permian probably comprises a shallow marine conglomerate overlaid by limestone and possibly by evaporites (salt deposits), and a black shale which could be a good source rock (called the Ravnefjell Formation in Greenland).

Continental fluvial deposits dominate the Triassic, with some marine elements – particularly on the Greenland side. A marine environment prevails on both Norwegian and Greenland sides, comprising evaporite deposits in the Middle to Upper Triassic. An older marine element also found on the Greenland side contains a black shale with source rock potential. This could be a southerly equivalent of the source rocks in the Botnheia Formation in Svalbard. The Triassic sedimentary successions in the JMM are expected to be most similar to the corresponding strata in eastern Greenland.

A regional sea-level rise and transgression began over the whole area in the Early Jurassic. That led during the Jurassic to the creation of a permanent link between the Boreal Sea to the north and the Tethys Sea to the south. Most of this period, from the Middle Jurassic and throughout the Upper Jurassic, coincided with the Kimmeridgian rift phase between Scandinavia and Greenland. That produced a landscape with the uplift of regional domes and riftvalley edges during the Middle Jurassic, followed by the collapse and inundation of the whole rift system in the Late Jurassic and Early Cretaceous. In this landscape, large delta systems developed in the Middle Jurassic and associated clastic coastal sediments were deposited to form Norway’s most important reservoir rocks.

A special feature of the Jurassic is that the succession of rock layers in the Lower and Middle Jurassic on the Halten Terrace and Trøndelag Platform are virtually identical with the succession in Greenland’s Jameson Land. The Upper Cretaceous and the bottom of the Lower Cretaceous are also virtually identical, with a succession of marine shales which, in their uppermost part, comprise the most important source rocks in the North Atlantic (the Spekk Formation on the Norwegian side and the Hareelv Formation on the Greenland side). This sedimentary succession also contains strata with good reservoir rocks, sandstones alternating with shale layers (the Rogn Formation, for example, which forms the reservoir rock in the Draugen field). More sandy elements of this kind appear to exist on the Greenland side than the Norwegian. The JMM lies midway between, so that the same Jurassic sedimentary succession is expected on both sides. As on both the Norwegian and the Greenland sides, however, parts of the JMM could also have formed small land areas without deposition during the Jurassic.

During the Cretaceous, the big basins between Scandinavia and Greenland (the Møre, Vøring, Harstad and Tromsø Basins) subsided deeply, and several thousand metres of sediment were deposited. The Cretaceous sedimentary succession in the platform and terrace areas along the flanks of these basins varies in thickness from a few hundred to just over a thousand metres. The JMM was probably part of the platform area on the western side of the Møre Basin during the Cretaceous, so that thicknesses and rocks in the sedimentary succession from this period will be similar to those found on the Trøndelag Platform and Halten Terrace and in Jameson Land – in other words, moderate thicknesses of marine shales with elements of thin sandstone strata.

The area was uplifted in the Palaeocene ahead of the last phase of crustal extension and the final continental separation between Greenland and Scandinavia. A considerable amount of sand together with shale was deposited on both Norwegian and Greenland sides during this period. Both sides show a marked hiatus in the mid-Palaeocene, where much of the Palaeocene succession is eroded or not deposited. The hiatus is greatest on the Palaeocene highs. In the lower-lying areas, it narrows into the Selandian (about 60 million years ago), which accordingly appears to be the period when this uplift occurred. Thereafter the area sank again, and shallow marine sands were deposited in a number of areas. It was uplifted again before the major vulcanism which began with the actual continental separation in the early Eocene. The basaltic lavas from this process are the oldest materials so far sampled on the JMM. How much Palaeocene sand has been preserved on the JMM is uncertain. The degree to which such sand has been preserved in eastern Greenland and on the Norwegian side varies a good deal. If present, the sand lies under lava layers.

The sedimentary successions under the lava layers in the Eocene could have a big oil and gas potential, particularly if the Jurassic succession is present at a favourable depth in the sub-surface. But the JMM experienced a powerful tectonic phase in the Oligocene which did not affect the NCS. That may have caused damage to and leaks from pre-existing petroleum traps, but could also have led to the formation of new traps. Mapping this part of the sedimentary succession with the aid of seismic images has been impossible because of the overlying lava layers.

 

Description of plays

Plays are defined on the basis of stratigraphic levels in the subsurface, reservoir rocks, petroleum trapping mechanisms and source rocks.

Three plays have been defined at two levels in the sub-surface on the Jan Mayen Ridge – the first two in the Eocene (east and west) and the third at a level of indeterminate age below the thick layers of basaltic lava beneath the Eocene (sub-basalt). While the strata under the lava are difficult to map, those in the Eocene show up well on the seismic images. This makes mapping much more assured. The two Eocene plays are distributed geographically on either side of the Jan Mayen Ridge, while the sub-basalt play covers the whole ridge.

 

Overview map showing the extent of the plays: east Eocene (green), west Eocene (red) and sub-basalt (green and red).

Figure 7.13 Overview map showing the extent of the plays: east Eocene (green), west Eocene (red) and sub-basalt (green and red).


 

Source rocks and migration

All three plays assume the migration of oil and/or gas from the same source rocks – shales in the Upper Jurassic, Middle Triassic and Middle Permian. It is uncertain how deeply these source rocks are buried or whether they are all present in the Jan Mayen Ridge. Maturation models show that, providing source rocks are available at a favourable burial depth, considerable opportunities exist for at least one to be still forming oil and/or gas. In that event, the petroleum traps in the sub-basalt play will be favourably placed for inward migration of petroleum because this level is closest to the source rock(s). Petroleum in the two Eocene plays has further to migrate because the Eocene lies higher up the succession and because the thick lava layers may act as a barrier to its ascent.

 

Reservoir rocks

Reservoir rocks in the Eocene plays are expected to comprise a clean, quartz-rich sandstone with good reservoir properties – in other words, high porosity and permeability. Samples of this sandstone show that it is indistinguishable from a corresponding Eocene sandstone in eastern Greenland, the Bopladsdalen Formation. It is accordingly reasonable to assume that the sandstone sampled on the Jan Mayen Ridge belongs to the same formation and is found across a wide area.

The sub-basalt play could contain sandstone reservoirs at several levels. The most probable are sandstones deposited in shallow water during the Triassic and/or Jurassic. These are expected to be equivalent to the very good reservoir rocks found at corresponding levels in Jameson Land in eastern Greenland and on the Halten Bank on the NCS.

 

Trap mechanisms

The two Eocene plays are distinguished from each other first and foremost by the type of trap mechanism. The traps in the west Eocene play comprise fault blocks which have been rotated and buried in tight shale. The sandstone strata are accordingly tilted and effectively sealed at the tips of the fault blocks, which provides good traps for petroleum migrating vertically. See figure 7.14. Faults forming such traps are generally distributed over the western parts of the Jan Mayen Ridge.

 

A seismic cross-section across the Jan Mayen Ridge, with the location of the plays discussed in the text marked.

Figure 7.14 A seismic cross-section across the Jan Mayen Ridge, with the location of the plays discussed in the text marked. The location is indicated by the red line on the inset map. This also shows the water depth (red = shallow, blue = deep) and the play outlines.

 

The eastern flank of the ridge, containing the east Eocene play, has few faults and strata slope evenly down towards the deepwater Ægir Basin to the east. Petroleum traps in this play are assumed to consist primarily of stratigraphic traps – in other words, places where the sandstone wedges out, surrounded by shale. Since the strata are sloping, such uptilted sandstone wedges will form traps sealed by the surrounding shale.

Because of the hard basalt layers, no detailed seismic image exists so far of the types of petroleum traps in the sub-basalt play. However, the faults in the strata above the lavas also run through the underlying strata and create rotated fault blocks there. Jurassic and older strata in eastern Greenland and on the Halten Bank were subject to tectonic faulting for a time before the lava layers were laid down. Rotated fault blocks are therefore likely to have formed petroleum traps throughout this play.

 

Resource evaluation

 

Methodology

Whether petroleum exists in an area is always uncertain. Calculating resources in plays takes account of this uncertainty by risk-assessing the various parameters which are significant for the presence and retention of petroleum. Plays are also defined with uncertainty distributions for different reservoir and liquid parameters.

Defining plays is a method for systematising and grouping the geological parameters which characterise the play and which distinguish it from other plays.

 

Results of the resource evaluation

Three plays have been defined in the Jan Mayen area. Two are in Eocene rocks (about 55-35 million years old), and one in older rocks lying beneath volcanic layers (the sub-basalt play). The two Eocene plays are distributed geographically on either side of the Jan Mayen Ridge, while the sub-basalt model covers the whole ridge (figure 7.14). The probability that all three plays have migration of oil and/or gas from the same source rock is high. An interdependence has accordingly been incorporated between the plays for the presence of source rock. In addition, an interdependence has been incorporated between the Eocene plays with regard to petroleum retention.

Expected recoverable resources from Jan Mayen are estimated at 90 million scm oe. Since mapping the strata beneath the basalt is difficult, it is very uncertain – particularly for the sub-basalt play – whether petroleum is present under these plays. This uncertainty is reflected in the resource distribution, with a downside of no discoveries (0 scm oe) and an upside (P05) of 460 million scm oe (five per cent probability that the resources are equal to or greater than 460 million scm oe). See figure 7.15. The probability of making one or more discoveries is 44 per cent.

 

Distribution of total recoverable resources in the Jan Mayen area. The right-hand graph shows the resource distribution if at least one discovery is made which confirms at least one play.

Figure 7.15 Distribution of total recoverable resources in the Jan Mayen area. The right-hand graph shows the resource distribution if at least one discovery is made which confirms at least one play.

 

The large uncertainty range reflects the fact that none of the plays in the Jan Mayen area has been confirmed. If at least one of the plays is confirmed through drilling, expected resources in the area would rise to about 200 million scm oe (see figure 7.15), with a downside (P95) of roughly 20 million scm oe and an upside (P05) of approximately 650 million scm oe.

Figure 7.16 presents the cumulative distribution of recoverable resources for the Jan Mayen area should at least one discovery be made which confirms at least one play. The figure shows the contributions from the various plays. It is the sub-basalt play which contributes to the high resource estimates.

 

Cumulative distribution of total recoverable resources in the Jan Mayen area, showing the contributions of the various plays, assuming that at least one discovery is made which confirms at least one play.

Figure 7.16 Cumulative distribution of total recoverable resources in the Jan Mayen area, showing the contributions of the various plays, assuming that at least one discovery is made which confirms at least one play.

 

Expected recoverable resources break down into about 70 million scm of liquids and roughly 20 billion scm of gas. Should at least one discovery be made which confirms at least one play, the resources break down into some 150 million scm oe of liquids and 50 billion scm of gas. See figure 7.17.

 

Cumulative distribution of total recoverable oil and gas resources in the Jan Mayen area, assuming that at least one discovery is made which confirms at least one play.

Figure 7.17 Cumulative distribution of total recoverable oil and gas resources in the Jan Mayen area, assuming that at least one discovery is made which confirms at least one play.

 

Estimates of undiscovered resources in the Jan Mayen area are very uncertain. A potential exists for oil and gas discoveries. The distribution between oil and gas is estimated to be 75 and 25 per cent respectively. A better understanding of how the plays function and a confirmation through discoveries could provide a substantial resource upside.

 

International chronostratigraphic chart