Prospectivity and Geological Overview

Under-explored with promising potential

West Greenland is significantly under-explored. Only seven wells have been drilled and the seismic coverage (less than 85,000 km 2-D seismic data in total) is still very regional for a potential petroleum province comparable in size to the to the Viking Graben–Central Graben system of the North Sea (Fig. 1.4). Exploration during the 1970s concentrated on areas where water-depths are less than about 500 m. During the 1970s, 37,000 km of 2-D seismic data were acquired and 5 wells were drilled (Hellefisk-1, Ikermiut-1, Kangâmiut-1, Nukik-1, and Nukik-2), all of them declared dry at the time.

Today‘s technology is more than adequate for exploration offshore West Greenland, an area with water-depths less than 1500m and fairly ice-free conditions. The results of the 6354/4-1 well (Qulleq-1) are not critical for exploration over the central and northern part of offshore West Greenland inside the licensing round acreage. Although the first major oil discovery has yet to be made, the seismic database allows us to postulate that the potential of West Greenland could be similar to the potential of the North Sea.

Two breakthroughs for prospectivity

Two breakthroughs in the late 1980s and early 1990s changed totally the appreciation of the hydrocarbon prospectivity of offshore southern and central West Greenland. The first breakthrough was the realisation that the sedimentary basins that could contain oil and gas were much larger than had been supposed in the 1970s (Chalmers & Laursen 1995, Chalmers et al. 1993). The second breakthrough was the discovery of extensive oil seeps in the onshore Nuussuaq Basin (Bojesen-Koefoed et al. 1999). The results of drilling in the 1970s had been interpreted as showing that the basins were only gas-prone, and the discovery of the oil demonstrated that this is wrong. So far, five distinct types of oil have been found, two of which could extend regionally over all or part of the offshore basins. Modern understanding suggests that the sedimentary basins offshore southern and central West Greenland cover an area of more than 200,000 km², which is larger than the combined Viking–Central graben system of the North Sea (Fig. 1.4).

The new understanding of the regional geology led to the acquisition of more than 30,000 km of 2-D seismic data during the 1990s in water depths up to 1500 metres. New licences were awarded offshore in 1996 (the Fylla licence with Statoil as operator) and 1998 (the Sisimiut-West licence with Phillips as operator), and during summer 2000 an exploration well  was drilled on the Fylla licence (6354/4-1 or Qulleq-1). Furthermore, grønArctic Energy held a licence onshore from 1995 to 1998 in the Nuussuaq area, and here  various forms of geophysical data were acquired and  several slim-holes drilled in 1994 and 1995. A full exploration well (GRO#3) was drilled in 1996. The well was declared dry but later quantitative log-interpretation by GEUS of the upper part of the well (which was not tested prior to casing) suggested high hydrocarbon saturations in sandstone units. Financial constraints forced this small company to relinquish its licence in 1998.

Reinterpretation by GEUS in 1997 of data from the Kangâmiut-1 well in the deepest part of the well suggests that oil may be present in syntectonic fan sediments (Bate 1997). During drilling such high pressures were encountered that it took nine day to control the well using very high mud weights. Gas was recorded consisting of C1 to C4 in measurable amounts and a trace of C5. A drill-stem test of the porous interval produced only water which, however, had the same chemistry as the drilling mud. It it thus possible that liquid hydrocarbons in the reservoir were simply flushed away, and therefore the prospectivity of the Kangâmiut Ridge was not fully evaluated by the well.

Sedimentary basins, structural elements and stratigraphy

The margin of West Greenland was formed by extensional opening of the Labrador Sea in late Mesozoic – early Cenozoic time. A complex of linked rift basins stretch from the Labrador Sea to northern Baffin Bay recording a scissor-like opening (Chalmers et al. 1993, Chalmers & Pulvertaft 2001). A conspicuos element of this tectonic framework is the Ungava transform fault system (Fig. 1.5). Disposal of the movement along this left-lateral wrench system was accomodated by numerous splays. Locally restraining bends along these splays have formed compressional structures (Chalmers et al. 1995).

Sedimentary basins, containing up to 8–10 km of sediments, are found primarily between 63°N and 68°N, which is the area to be offered for licensing in 2001. The oldest sediments in the basins may be of Early Cretaceous age (Chalmers et al. 1993), and the seismic data indicate at least two rifting events (Fig. 2.1). Finds of reworked Jurassic palynomorphs in the Qulleq-1 well suggest, however, that even older sediments may be present (see GHEXIS Newletter 19).

The first event, in the Early Cretaceous culminating in the Aptian–Albian, possibly formed one group of rotated fault-block plays. This was followed by thermal subsidence of the basin during the Late Cretaceous. In general, sedimentation in the basin centres appears to have been of fine-grained clastics during this period, but in places basin-marginal fans may have formed along faults and fault escarpments. A second rifting event took place in the Campanian–Paleocene and was probably associated with the start of sea-floor spreading in the Labrador Sea. This formed a second generation of fault-block plays.

The drift phase of sea-floor spreading in the Labrador Sea was generally accompanied by regional subsidence of the sedimentary basins. However, sediment input to the basins during Palaeogene times appears to have been high, especially in the Sisimiut Basin (Fig. 3.1). During especially the early part of that period, basin-floor fans as well as fans along active faults may have been deposited.

Sea-floor spreading in the Labrador Sea was transferred to Baffin Bay to the north along a complex strike-slip fault system, the Ungava Fault Zone, which may resemble the better-known San Andreas Fault System in California. Part of this system in Greenland waters between 66°N and 68°N is in transpression, where it forms flower structures known as the Ikermiut Fault Zone (Fig. 3.1).

Initial opening of the Labrador Sea was accompanied by voluminous volcanism, probably associated with the impact of the Iceland plume. The largest area of volcanic rocks is found north of 68°N and it extends onshore into the Nuussuaq Basin. Other areas of volcanism are found farther south on the Nukik Platform and on the Hecla and Maniitsoq Rises (Figs 3.1 and 3.8).

Thermal subsidence of the basin continued after cessation of sea-floor spreading in the Labrador Sea, probably in Middle or Late Eocene time, but there appears to have been an episode of uplift of the basin margin in the Neogene. The northeastern part of the Sisimiut Basin is especially affected by this uplift, and the onshore Nuussuaq Basin probably owes its present-day exposure to it.

Regional structure

The Palaeogene volcanic rocks that are exposed on Disko, Nuussuaq and Svartenhuk Halvø are known to extend offshore. Their southern limit is just south of the Hellefisk-1 well, where they were drilled  (Rolle 1985) (Fig. 3.1).

Southeast of the volcanics is the deep Sisimiut Basin (Fig. 3.1 and 3.2). The northern parts of the Sisimiut Basin have been uplifted and eroded in relatively recent geological times (Chalmers 2000), possibly as late as Miocene or even Pliocene, and the eastern border of the Sisimiut Basin is a major fault, so close to the coast that many of the seismic lines do not cross it because of skerries composed of basement.

The Sisimiut Basin is bounded to the west, northwest and north by the tectonically disturbed Ikermiut Fault Zone (Fig. 3.1 and 3.2). This structure is interpreted as a major strike-slip fault zone that is locally in transpression, forming flower structures (Chalmers et al. 1995). The Sisimiut-West licence area is over part of the Ikermiut Faul Zone.

West of the Ikermiut Fault Zone is a shallow basin exhibiting synclinal folding (Fig. 3.1 and 3.2), and west of that is the shallow to outcropping basement of the Davis Strait High (Srivastava 1983), which consists probably of continental basement at or near the seabed.

To the southeast of the Sisimiut Basin is the Nukik Platform, an area of shallow basement and volcanics drilled by the Nukik-1 and Nukik-2 wells (Figs 3.1, 3.3 and 3.4).

The Sisimiut Basin is separated from the Nuuk Basin (Figs 3.1, 3.4, 3.5, 3.6 and 3.7) by three en-echelon basement ridges between 65º 30‘N and 66º 20‘N. The middle of the three, the Kangâmiut Ridge (Figs 3.1 and 3.3), was drilled by the Kangâmiut-1 well (Rolle 1985). Fault-blocks visible on the western part of Fig. 3.2 are on the eastern margin of the Davis Strait High which is entirely in Canadian waters at the latitude of this line.

The northern Nuuk Basin is flanked to the east by the Nukik Platform and to the west by the shallow basement/volcanic complex here termed the Maniitsoq Rise (Figs 3.1 and 3.4). The western margin of the Maniitsoq Rise consists of westward-facing fault blocks (Fig. 3.4).

The southern limit of the Nukik Platform is at approximately 65°N, south of which is an area of fault-blocks here termed the Atammik Structural Complex (Figs 3.1, 3.5 and 3.6). Southwest of the Atammik Structural Complex, and partly separated from it by an area of shallow basement, is the Fylla Structural Complex (Fig. 3.1 and 4.4.2) over part of which is the Fylla licence area. South-east of the Fylla Structural Complex is another faulted area with a different structural style. Much of this area is under water depths greater than 1000 metres.

A major SSW–NNE-trending fault separates the Atammik and Fylla Structural Complexes from the Nuuk Basin to the west (Figs 3.1 and 3.5). The southern part of the Nuuk Basin is bordered to its west by the shallow basement and volcanic Hecla Rise (Tucholke & Fry 1985) (Fig. 3.1 and 3.7). The western part of the Hecla Rise consists of large fault-blocks  that step down to the Lady Franklin Basin (Fig. 3.1 and 3.7), most of which is in Canadian waters.

An area of faulting, partly of block-faults and partly of more complex character, stretches all the way along the Canadian margin west of the Hecla Rise and Maniitsoq Rise (Figs 3.1, 3.4 and 3.5).

Stratigraphy

The stratigraphically deepest well offshore West Greenland (Qulleq-1) has only penetrated mid-Cretaceous sediments (Ghexis Newsletter 19) referred to the Kangeq sequence (Fig. 2.1; Chalmers et al. 1993, Chalmers et al. 1995). On the seismic data, several deeper seismic sequences (Appat, Kitsissut and ‘Deep‘ sequences) can be seen that may contain possible reservoirs and seals. Recent  biostratigraphy (Nøhr-Hansen 1998) has shown that the regional mid-Cenozoic unconformity depicted in Chalmers et al. (1995) and  Chalmers et al. (1993) to be at the end of the Eocene is, in fact, between the Lower and Middle Eocene.

Various basalt units of both Paleocene and early Eocene age that are the stratigraphic equivalents of the Palaeogene sedimentary interval can be mapped in the region between 63°20'N and 66°15'N and north of 67°40'N (Fig. 3.8).