Play Types

Leads and prospects of several different play types have been identified in the basins and many more are expected to be found as data density increases. The main play types hitherto identified are:

• Upper Cretaceous fault blocks (prospects similar to those seen in the Fylla Licence)
• Traps related to compressional structures in the Ikermiut Structural Complex
• Hanging-wall and basin-floor fans and similar traps in Upper Cretaceous, Paleocene and Lower Eocene sediments
• Fault-block traps in the Appat and Kitsissut sequences

Nunaoil and GEUS have carried out a preliminary prospect evaluation study in the Kangâmiut Ridge area based on the existing seismic data. Several large prospects have been evaluated (see poster as pdf-file; 1600 kB). Nunaoil can present the prospect evaluation to interested companies.

Upper Cretaceous fault block play (Fylla-type)

In the licensing round area, Upper Cretaceous sediments show large-scale 4-way closures in the order of 200 km² to 400 km². On Fig. 4.4.2 on of the prospects within the Fylla Structural Complex region is shown. Fault block prospects, similar to those seen in the Fylla area can be seen west of the Hecla and Maniitsoq Rises and in the area south of the Fylla area (Fig. 3.1). Cross-sections through some of these structures are shown in Figs 4.4.4 and 4.4.5. This play needs, however, to be re-evaluated as a consequence of the results of the 6354/4-1 well in the Fylla area; see GHEXIS Newsletter 19, a pre-print of a paper for 'Review of Greenland activities 2000' (in pdf-format, 1900 kB) and a summary by the Statoil Group on the drilling results (in pdf-format, 287 kB).

Strike-slip-fault related plays (Sisimiut-type)

Extensional opening of the Labrador Sea and Baffin Bay during the Paleocene and Eocene was transferred along a complex of strike-slip faults that form the Ungava Fault Zone (see Fig. 1.5; Chalmers & Laursen 1995, Chalmers et al. 1993). Part of the Ungava Fault zone forms the Ikermiut Fault Zone (Figs 3.1 and 4.5.1).

Fig. 4.5.2 shows a cross-section through the Ikermiut Fault Zone. The cross-section shown here forms a flower structure and the Ikermiut-1 well was drilled on a fold on the eastern flank of the structure. The area between the faults is compressed, rotated and uplifted in folds and thrust faults.

The Ikermiut-1 well drilled through Lower Eocene, Paleocene and Kangeq sediments consisting entirely of mudstones. No reservoir was found. If a Cenomanian–Turonian oil source rock exists in the Sisimiut Basin, it will be up to 1 km deeper than the well reached, and should be mature in this area (see section on Source Rocks). Oil expelled from a source rock could migrate into reservoirs in Appat/Kitsissut sediments along the Ikermiut Fault Zone.

The transpressional structures of the Ikermiut Fault Zone continue north of the Sisimiut-West licence, one branch being due north to the area of the Hellefisk-1 well, and a second branch running northeastwards (Fig. 3.1). The northern branch was tested by the Hellefisk-1 well, but no hydrocarbons were found. The well terminated after drilling more than 500 metres of Paleocene basalts (Rolle 1985). Little interpretable seismic energy is visible from below the basalts.

A section through the northeast branch is shown in Fig. 4.5.3, which shows Appat/Kitsissut and Paleocene sediments faulted and folded into a structure that might be capable of trapping hydrocarbons. Much more seismic data would be needed to map any traps.

Hanging-wall fans and similar traps in upper Cretaceous, Paleocene and Lower Eocene sediments

Kangâmiut Ridge

The Kangâmiut-1 well was drilled on the west flank of a basement ridge, the Kangâmiut Ridge (Figs 4.6.1). The well was drilled through a Recent to Middle Eocene succession composed predominantly of sandstone, then a Lower Eocene to Paleocene succession which was entirely mudstone (Rolle 1985, Fig. 4.6.1). Interpretation of the section below 3674 metres is controversial. The uppermost 26 m consists mostly of sandstone with some mudstone. Below 3840 metres the well entered basement. The section between 3700 metres and 3840 metres has been interpreted as consisting either of a syn-tectonic fan containing large boulders of kaolinised basement or as fractured, kaolin-weathered basement (cf. Bate 1997, Chalmers 1992).

High pressures were encountered in the section below 3706 metres that necessitated the use of very heavy control mud. Repeated circulation over a period of 9 days with increasingly dense muds eventually brought the well under control with a mud weight (S.G.) of 1.82 (14.4 lbs/gal.). During circulation of the kill muds, gas-chromatograph readings of up to 9% were recorded with the gas consisting of C1 to C4 in measurable amounts and a trace of C5 (Bate 1997). Such readings commonly indicate that the well has penetrated an oil field, or at least a gas condensate field. A Drill-Stem Test (DST) performed over the interval 3674 to 3705 m flowed 29 m³ of water during a total period of 2 hrs 10 minutes, after which flow ceased. Later testing of the water showed that it had the same chemistry as the drilling-mud fluids. The evidence strongly indicates that Kangâmiut-1 drilled through an oil or condensate accumulation, but that during the operations to control the high pressures, the hydrocarbons were flushed away from the volume around the well, the annulus was sealed by drilling mud solids, and only drilling-mud liquids were produced during the DST.

The large thickness (140 m) of the kaolinised interval makes it unlikely that this consists of in situ weathered basement. Such thicknesses of kaolinised weathering are found only in the tropics, and the Kangâmiut Ridge has never been in tropical latitudes since the basal sediments were laid down in either the Santonian (Nøhr-Hansen 1998) or Paleocene (Bate 1997).

A search along the flanks of the Kangâmiut Ridge located a seismic anomaly that could be a second fan, substantially larger than the one penetrated by Kangâmiut-1. The seismic anomaly consists of relatively high amplitude reflections near the Paleocene–Eocene boundary. A dip-section through the anomaly is shown in Fig. 4.6.3 and a strike section shows the topography of the basement surface to be irregular with ridges and valleys. The dip sections show that these features must dip steeply to the west. Nonetheless, other data indicate that it is possible that the location of the fan is controlled by topography, and that the fan-sands were deposited in a valley. Two hypotheses for the depositional environment of the sands are that they could be a basin-floor fan fed by turbidites or a transgressive, shallow-water, near-coastal system preserved only in the valley.

Recently, Nunaoil and GEUS have carried out a preliminary prospect evaluation study in the Kangâmiut Ridge area based on the existing seismic data. Several large prospects have been evaluated (see poster as pdf-file - 1600 k).

Nukik Fan

The presence of an area of thick prograding sediments on the northwest corner of the Nukik Platform has been known for many years (Ottesen 1991, Henderson et al. 1981).

Three seismic sequences, all of which consist of low-stand sediments, which can be divided into sediments deposited on a shelf, on a slope and in deep water beyond the foot of the slope (Fig. 4.6.6). Indications of basin floor fans can be found within the deep-water sediments, and these fans could trap hydrocarbons.

A map over the extent of the fans within one (the deepest) of the sequences is shown in Fig. 4.6.7, together with the locations of the existing seismic data. The fans may be large, extending possibly for several tens of kilometres in a SW–NE direction; in which case there could be large volumes of hydrocarbons trapped within them.

Regional correlation shows that the prograding structures are of Late Cretaceous (Kangeq Sequence) age. The possible Cenomanian–Turonian Source rock could lie at the base of the prograding system and be mature at the present-day (see section on Source Rocks). If so, the migration route from the source rock to the fans is very short and direct.

Other hanging-wall fans

The leads described at the Kangâmiut Ridge and Nukik Fan are examples of hanging-wall fans, where sand or coarser sediment has been deposited on the hanging wall of either an active fault or a fault escarpment. A number of areas where such sediments may have been deposited during the Late Cretaceous, Paleocene or early Eocene, have been identified.

Examples of a number of candidates for hanging wall fans are shown in Figs 4.6.10 and 4.6.11. New seismic data acquired in 2001 by the Statoil group in the western Fylla area demonstrates closures at several levels in the Cretaceous succession, primarily as roll-overs formed by later compression along the main Fylla fault (see GHEXIS Newsletter 20). The seismic data is now available from GEUS.

Examples of the types of area where additional examples of hanging-wall fans may be found are shown in semi-regional cross-sections 4.6.12 and 4.6.13. Both sections show similar structural environments; 4.6.12 in the area west of the Hecla Rise, and 4.6.13 across the Atammik Structural Complex.

Lower–Middle? Cretaceous fault block prospects (Appat and Kitsissut sequences)

The Appat and Kitsissut sequences have been dated by analogy with the Upper and Lower Members of the Bjarni Formation of the Labrador Basin (Balkwill 1987). There, the Bjarni Formation forms the main reservoir within which substantial amounts of gas have been discovered in the Bjarni and North Bjarni Fields and by the Hopedale E-33 well. The Upper Bjarni Member, possibly equivalent to the Appat Sequence, consists of sandy, clayey and carbonaceous, marine in part but predominantly nonmarine, siltstone and shale, with intercalated beds of feldspathic, partly porous sandstone. The Lower Bjarni Member, possibly equivalent to the Kitsissut Sequence, consists of feldspathic, lithic, coaly, in part conglomeratic, fine- to coarse-grained nonmarine quartzose sandstones, with poor to excellent intergranular porosity (Balkwill et al. 1990).

The Appat and Kitsissut sequences can  be distinguished only locally and therefore no distinction has been made between them on the map showing the top of the combined unit. The only trapping configuration found using the Appat/Kitsissut as reservoir is fault blocks. A number of specific leads and prospects have been identified.

Fylla Structural Complex

Within the Fylla area closed structures with sandstones at top Appat/Kitsissut level can be mapped. A cross-section of a Appat/Kitsissut prospect is shown in Fig. 4.7.2.

Atammik Structural Complex

A closed structure at top Appat/Kitsissut level was described by Chalmers et al. (1993, fig. 19) based on interpretation of seismic data from the 1970s. New seismic data confirm the existence of a closed structure at basement level (Fig. 4.7.4). A cross-section through the lead is shown in Fig. 4.7.5.

Southern Nuuk Basin

Two leads have been found in the southern Nuuk Basin using widely-spaced regional lines. A cross-section through one of them is shown in Fig. 4.7.6.

Other possibilities

Fault-block leads of the type described above may be found in other parts of the Atammik Structural Complex in addition to the lead described above. Fig. 4.7.7 shows a cross-section through the area, which shows a number of fault blocks that could be prospective.

The other area where leads may be found is west of the Hecla and Maniitsoq Rises, and Fig. 4.7.8 shows a cross-section through that area.