Geological Survey of Denmark and Greenland Bulletin 13, 2007
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Review of Survey activities 2006, 25-28 |
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A detailed geophysical mapping project has been carried out
by the Geological Survey of Denmark and Greenland
(GEUS) in the offshore region south-west and west of Disko
and Nuussuaq, central West Greenland as part of the prepa-
rations for the Disko West Licensing Round in 2006 (Fig. 1).
The main purpose of the study was to evaluate the prospec-
tivity of this almost 100 000 km
by the Geological Survey of Denmark and Greenland
(GEUS) in the offshore region south-west and west of Disko
and Nuussuaq, central West Greenland as part of the prepa-
rations for the Disko West Licensing Round in 2006 (Fig. 1).
The main purpose of the study was to evaluate the prospec-
tivity of this almost 100 000 km
2
large region, and to increase
knowledge of basin evolution and the structural develop-
ment. Results of the work, including a new structural ele-
ments map of the region and highlights of particular interest
for hydrocarbon exploration of this area, are summarised
below.
ment. Results of the work, including a new structural ele-
ments map of the region and highlights of particular interest
for hydrocarbon exploration of this area, are summarised
below.
Evidence of live petroleum systems has been recognised in
the onshore areas since the beginning of the 1990s when
seeps of five different oil types were demonstrated (Bojesen-
Koefoed et al . 1999). Oil seeps suggesting widely distributed
marine source rocks of Mesozoic age are particularly promising
for the exploration potential (Bojesen-Koefoed et al . 2004,
2007). Furthermore, possible DHIs (Direct Hydro carbon
Indicators) such as gas-clouds, pock marks, bright spots and
flat events have been interpreted in the offshore region
(Skaarup et al . 2000; Gregersen & Bidstrup in press).
seeps of five different oil types were demonstrated (Bojesen-
Koefoed et al . 1999). Oil seeps suggesting widely distributed
marine source rocks of Mesozoic age are particularly promising
for the exploration potential (Bojesen-Koefoed et al . 2004,
2007). Furthermore, possible DHIs (Direct Hydro carbon
Indicators) such as gas-clouds, pock marks, bright spots and
flat events have been interpreted in the offshore region
(Skaarup et al . 2000; Gregersen & Bidstrup in press).
The evaluation of the region (Fig. 1) is based on all public
and proprietary seismic data together with public domain mag -
netic and gravity data. The seismic data (a total of c . 28 000
line km) are tied to the two existing offshore exploration
wells in the region (Hellefisk-1 and Ikermiut-1). The study
also incorporates information on sediments and volcanic
rocks from onshore Disko and Nuussuaq (Fig. 2).
netic and gravity data. The seismic data (a total of c . 28 000
line km) are tied to the two existing offshore exploration
wells in the region (Hellefisk-1 and Ikermiut-1). The study
also incorporates information on sediments and volcanic
rocks from onshore Disko and Nuussuaq (Fig. 2).
Ten seismic horizons ranging from `mid-Cretaceous' to
`Base Quaternary' (Fig. 2) have been interpreted regionally.
Large correlation distances to wells, varying data quality and
a thick cover of basalt in the north-eastern part of the region,
add uncertainty in the regional interpretation, especially for
the deeper horizons such as the `mid-Cretaceous' equivalent
to Santonian sandstone interval drilled in Qulleq-1 far south.
Large correlation distances to wells, varying data quality and
a thick cover of basalt in the north-eastern part of the region,
add uncertainty in the regional interpretation, especially for
the deeper horizons such as the `mid-Cretaceous' equivalent
to Santonian sandstone interval drilled in Qulleq-1 far south.
Based on the seismic interpretation (Fig. 3) structural ele-
ments maps, horizon-depth maps and isopach maps have
been produced; these maps, together with general strati-
graphic knowledge on potential reservoirs, seals and source
rocks (Fig. 2), provide important information for discussions
of critical play elements including kitchens and structures.
been produced; these maps, together with general strati-
graphic knowledge on potential reservoirs, seals and source
rocks (Fig. 2), provide important information for discussions
of critical play elements including kitchens and structures.
The existence of many large structures combined with the
evidence of live petroleum systems has spurred the recent
major interest for hydrocarbon exploration in the region.
evidence of live petroleum systems has spurred the recent
major interest for hydrocarbon exploration in the region.
Structural development
and basin evolution
and basin evolution
A number of deep basins with Cretaceous and Cenozoic sed-
imentary successions have been recognised offshore West
Greenland since the 1970s (e.g. Chalmers et al . 2001). In
Early to mid-Cretaceous times a number of major structural
complexes and basins developed in the region (Figs 1, 3),
mainly as a result of extensional faulting. These include the
imentary successions have been recognised offshore West
Greenland since the 1970s (e.g. Chalmers et al . 2001). In
Early to mid-Cretaceous times a number of major structural
complexes and basins developed in the region (Figs 1, 3),
mainly as a result of extensional faulting. These include the
© GEUS, 2007.
Geological Survey of Denmark and Greenland Bulletin
13, 25-28. Available at:
www.geus.dk/publications/bull
25
Petroleum systems and structures offshore central West
Greenland: implications for hydrocarbon prospectivity
Greenland: implications for hydrocarbon prospectivity
Ulrik Gregersen, Torben Bidstrup, Jørgen A. Bojesen-Koefoed, Flemming G. Christiansen,
Finn Dalhoff and Martin Sønderholm
Fig. 1. Structural elements offshore the Disko-Nuussuaq region, central
West Greenland. The position of the seismic example in Fig. 3 is shown.
Aasiaat Structural Trend, the Kangerluk
Structure, the Aasiaat Basin, the Sisimiut
Basin and the Nagssugtôq Subbasin (Fig.
1). Deep-seated fault-bounded basins lo -
cally showing anticlinal structures are
occasionally observed below the inter-
preted `mid-Cretaceous' seismic hori-
zon. Seabed sampling has shown the
presence of Ordovician carbonate strata
on the Davis Strait High (Dalhoff et al .
2006). Together with reworked Jurassic
or older palyno morphs observed in the
Qulleq-1 well farther south (Nøhr-
Hansen et al . 2000) these suggest the
possibility of pre-Cretaceous strata in
the deepest parts of these basins. Based
on outcrop studies, regional Cretaceous
sand-prone units are expected to be pre-
sent in the offshore region, both as
Structure, the Aasiaat Basin, the Sisimiut
Basin and the Nagssugtôq Subbasin (Fig.
1). Deep-seated fault-bounded basins lo -
cally showing anticlinal structures are
occasionally observed below the inter-
preted `mid-Cretaceous' seismic hori-
zon. Seabed sampling has shown the
presence of Ordovician carbonate strata
on the Davis Strait High (Dalhoff et al .
2006). Together with reworked Jurassic
or older palyno morphs observed in the
Qulleq-1 well farther south (Nøhr-
Hansen et al . 2000) these suggest the
possibility of pre-Cretaceous strata in
the deepest parts of these basins. Based
on outcrop studies, regional Cretaceous
sand-prone units are expected to be pre-
sent in the offshore region, both as
deltaic and shallow-marine deposits and as turbidite
deposits (Fig. 2).
deposits (Fig. 2).
During the Late Cretaceous a new rifting episode was
initiated and was characterised by normal faulting, subsi-
dence and syn-rift sedimentation including deposition of
a thick mudstone succession of Campanian-Maa strich -
tian age (Dam et al . 2000). This phase lasted into Early
Paleocene times resulting in repeated erosion and filling
of subaerial valley and submarine canyons and formation
dence and syn-rift sedimentation including deposition of
a thick mudstone succession of Campanian-Maa strich -
tian age (Dam et al . 2000). This phase lasted into Early
Paleocene times resulting in repeated erosion and filling
of subaerial valley and submarine canyons and formation
26
Fig. 2. Simplified stratigraphic scheme with
lithology from present coastal areas of Disko
and Nuussuaq (north), and from offshore
West Greenland wells towards the south. The
main phases of tectonism and subsidence are
listed. The main interpreted seismic horizons
are Seabed, Base Quaternary (
BQ
), mid-
Miocene (
MM
), Lower Eocene (
LE
), Top
Basalt 3 (
TB3
), Upper Paleocene (
UP
), Top
Basalt 2 (
TB2
), Top Basalt 1/Base Basalt 2
(
TB1
), Top Cretaceous (
TC
), mid-Cretaceous
(
MC
) and unspecified deep reflections.
The most likely intervals with source rocks
(
SO
), reservoir sands (
R
) and seals (
SE
) are
also indicated.
Fig. 3. Seismic section (GGUi95-17) through eastern parts of the
study region, showing main structural elements. The main
structural elements are from west to east: The easternmost parts of
the Aasiaat Basin, the Ilulissat Graben Edge (
IGE
), the Ilulissat
Graben on both sides of the Ilulissat High, and the westernmost
part of the Disko High. Note the amplitude anomalies above the
Ilulissat High (see Fig. 1 for location).
of regional unconformities (Dam &
Sønderholm 1998; Dam 2002).
Sønderholm 1998; Dam 2002).
A zircon age provenance study of
sandstone units in outcrops and off-
shore exploration wells indicates that
most of the sand units show local age sig -
natures characteristic of the Green land
shield to the east. However, a Gren ville
age component of probable Can a dian
derivation also seems to be present in
the deep-water deposits of the Nuus -
suaq Basin and in the Qulleq-1 well
suggesting a long-shore transport com-
ponent (Scherstén & Sønderholm 2007
- this volume).
shore exploration wells indicates that
most of the sand units show local age sig -
natures characteristic of the Green land
shield to the east. However, a Gren ville
age component of probable Can a dian
derivation also seems to be present in
the deep-water deposits of the Nuus -
suaq Basin and in the Qulleq-1 well
suggesting a long-shore transport com-
ponent (Scherstén & Sønderholm 2007
- this volume).
During the Paleocene-Eocene a
major episode of volcanic eruption took
place, and some hundreds of metres of
thick basalts cover part of the offshore
region (Fig. 3). The basalts may reach
thicknesses of more than 2 km in the
north-eastern offshore part of the study
region. However, the current mapping
suggests that the volcanic succession is
thinner and less widely distributed than
suggested in previous publications and
maps (e.g. Chalmers et al . 1993;
Chalmers & Pulvertaft 2001; Skaarup 2002). Strike-slip
movements during the Late Paleocene and Early Eocene
caused local transpression of structures primarily along the
Ikermiut Fault Zone, and locally in the basins and structures
farther north, contemporaneous with subsidence in the
Ikermiut Basin region. Transtensional and extensional move-
ments farther to the north-east, subsequent to the extrusion
of the Paleocene basalts, resulted in the development of the
more than 200 km long Ilulissat Graben (Fig. 1).
place, and some hundreds of metres of
thick basalts cover part of the offshore
region (Fig. 3). The basalts may reach
thicknesses of more than 2 km in the
north-eastern offshore part of the study
region. However, the current mapping
suggests that the volcanic succession is
thinner and less widely distributed than
suggested in previous publications and
maps (e.g. Chalmers et al . 1993;
Chalmers & Pulvertaft 2001; Skaarup 2002). Strike-slip
movements during the Late Paleocene and Early Eocene
caused local transpression of structures primarily along the
Ikermiut Fault Zone, and locally in the basins and structures
farther north, contemporaneous with subsidence in the
Ikermiut Basin region. Transtensional and extensional move-
ments farther to the north-east, subsequent to the extrusion
of the Paleocene basalts, resulted in the development of the
more than 200 km long Ilulissat Graben (Fig. 1).
During the Eocene, and especially during the late Mio -
cene to Pliocene, the offshore basins subsided rapidly, and
large sedimentary wedges prograded towards the west and
south, possibly as a consequence of Neogene uplift in the
pres ent onshore areas to the east (Fig. 3; Dalhoff et al . 2003;
Japsen et al . 2005; Bonow et al . 2007 - this volume).
large sedimentary wedges prograded towards the west and
south, possibly as a consequence of Neogene uplift in the
pres ent onshore areas to the east (Fig. 3; Dalhoff et al . 2003;
Japsen et al . 2005; Bonow et al . 2007 - this volume).
Petroleum systems and prospectivity
Based on seismic interpretation, depth conversion using seis-
mic velocities, sonic log data from the wells and the thermal
maturity gradient from selected wells, the most likely source
rock intervals (mid-Cretaceous and Lower Paleocene) seem
to be mature in large parts of the region (Fig. 4), though seis-
mic interpretation is difficult.
mic velocities, sonic log data from the wells and the thermal
maturity gradient from selected wells, the most likely source
rock intervals (mid-Cretaceous and Lower Paleocene) seem
to be mature in large parts of the region (Fig. 4), though seis-
mic interpretation is difficult.
In particular the Aasiaat Basin, the Aasiaat Structural
Trend, the North Ungava Basin, the Ikermiut Basin, the
Sisimiut Basin and the Ilulissat Graben (Fig. 1) may have ade-
quate dimensions and depths to have potential as kitchens for
hydrocarbon generation, with the potential also depending on
factors such as source rocks being present in sufficient qual-
ity and quantity. This study indicates that the interpreted
Sisimiut Basin and the Ilulissat Graben (Fig. 1) may have ade-
quate dimensions and depths to have potential as kitchens for
hydrocarbon generation, with the potential also depending on
factors such as source rocks being present in sufficient qual-
ity and quantity. This study indicates that the interpreted
27
Fig. 4. Simplified prospectivity map. Cretace -
ous to Palaeogene structures and major mid-
Cretaceous 4-way dip closures to the west,
pos sible hydrocarbon migration pathways and
mid-Cretaceous hydrocarbon generation areas
(maturity levels - early to main oil: ~0.5 ->
1%
R
o
; late oil: ~1 ->
1.3% R
o
; gas:>
1.3% R
o
).
28
source rock intervals possibly came into the oil window after
mid-Miocene time, subsequent to the formation of the main
structural closures providing a favourable timing for charging.
mid-Miocene time, subsequent to the formation of the main
structural closures providing a favourable timing for charging.
In the interpreted Cretaceous and Cenozoic sections,
amplitude anomalies are locally observed and may be inter-
preted as DHIs (such as e.g. bright spots above the Ilulissat
High in Fig. 3) that could be caused by trapped hydrocarbon.
Clusters of DHIs are located especially over or near the sup-
posed Cretaceous kitchen areas, and also locally where satel-
lite slicks have been recorded (Fig. 4), and contribute to an
indication of live petroleum systems in the offshore region.
preted as DHIs (such as e.g. bright spots above the Ilulissat
High in Fig. 3) that could be caused by trapped hydrocarbon.
Clusters of DHIs are located especially over or near the sup-
posed Cretaceous kitchen areas, and also locally where satel-
lite slicks have been recorded (Fig. 4), and contribute to an
indication of live petroleum systems in the offshore region.
Mapping of the Cretaceous and Palaeogene intervals and
structural highs has revealed many structures. Large struc-
tural closures can be outlined both in the western part of the
region (in the Aasiaat Basin, the Aasiaat Structural Trend and
the Kangerluk Structure), in the eastern part of the region
(both along the edge and within the Ilulissat Graben) and in
the southern part of the region related to the Ikermiut Fault
Zone (Fig. 4). The Cretaceous and Palaeogene structural clo-
sures are situated close to supposed kitchen areas (Fig. 4), and
together with the oil seeps and reservoir quality sandstones
known onshore and their supposed offshore equivalents,
these elements indicate that the offshore area west and south
of Disko could potentially be prospective.
tural closures can be outlined both in the western part of the
region (in the Aasiaat Basin, the Aasiaat Structural Trend and
the Kangerluk Structure), in the eastern part of the region
(both along the edge and within the Ilulissat Graben) and in
the southern part of the region related to the Ikermiut Fault
Zone (Fig. 4). The Cretaceous and Palaeogene structural clo-
sures are situated close to supposed kitchen areas (Fig. 4), and
together with the oil seeps and reservoir quality sandstones
known onshore and their supposed offshore equivalents,
these elements indicate that the offshore area west and south
of Disko could potentially be prospective.
Acknowledgements
The geophysical study was supported by the Bureau of Minerals and
Petroleum, Government of Greenland. TGS-NOPEC and NUNAOIL A/S
are thanked for permission to publish the structural maps that incorpo-
rate proprietary seismic and satellite slick data.
Petroleum, Government of Greenland. TGS-NOPEC and NUNAOIL A/S
are thanked for permission to publish the structural maps that incorpo-
rate proprietary seismic and satellite slick data.
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Authors' address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail:
ug@geus.dk
