Geological Survey of Denmark and Greenland Bulletin 38, 2017, 49-52 49 The onshore Nuussuaq Basin in West Greenland is impor- tant for hydrocarbon exploration since many of the key pe- troleum systems components are well exposed and accessible for study. The basin has thus long served as an analogue for offshore exploration. The discovery of oil seeps on Disko, Nuussuaq, Ubekendt Ejland, and Svartenhuk Halvø (Fig. 1) in the early 1990s resulted in exploration onshore as well. In several wells, oil stains were observed in both the siliciclastic sandstone and in the volcanic series. An important aspect of any petroleum system is a high quality reservoir rock. The aim of this paper is to review petrophysical aspects of the reservoir potential of key stratigraphic intervals within the Nuussuaq and West Greenland Basalt groups. Reservoir parameters and porosity–permeability trends for potential siliciclastic and volcanic reservoirs within the relevant for- mations of the Nuussuaq Basin are discussed below. Geological setting The Nuussuaq Basin formed in the Cretaceous–Palaeogene as part of a complex system of linked rift basins that developed along West Greenland during the opening of the Labrador Sea and Baffin Bay (Oakey & Chalmers 2012). As a result of Neogene uplift, the sediments and overlying Palaeogene volcanic rocks are exposed on Disko, Nuussuaq, Upernivik Ø and Svartenhuk Halvø (Fig. 1, Dam et al. 2009). The sedimentary succession is interpreted as deposited in fluvial, delta, shelf and deep marine environments, and is divided into ten formations forming the Nuussuaq Group (Fig. 2). The overlying West Greenland Basalt Group (WGBG) in- cludes subaerial lava flows and hyaloclastite breccias (Larsen et al. 2016). A companion paper to this contribution (Søren- sen et al. 2017, this volume) provides additional information regarding the structural development and potential source rock distribution of the Nuussuaq Basin. Potential hydrocarbon reservoirs of Albian–Paleocene age in the Nuussuaq Basin, West Greenland Morten L. Hjuler, Niels H. Schovsbo, Gunver K. Pedersen and John R. Hopper Halvø Ubekendt Ejland Uummannaq D i s k o N u u s s u a q Upe rniv ik Ø Ik KQ It GRO GW GT FP93 Ma Um FP94 AK GK GE PK An Ki Qi IkKa RK Uk AK Pi Well Outcrop Nuussuaq Group Quarternary units Basement Ice sheet Fault Oil shows West Greenland Basalt Group FormationOutcrop Member Ki Ka Atane Kangilia Kingittoq Kangilia Kingittoq Annertuneq Congl. Pi AK Ik GGU247801 Ikorfat fault 566 m Atane - Cores Formation LogsWell Faults AtanePingu Skansen AK FP93 It FP93-3-1 Itilli fault zone 139 m Atane - KangiliaAtaata Kuua Qilakitsoq FP94 KQ FP94-11-04 Kuugannguaq-Qunnilik fault 340 m Itilli - Qi RK GE GANE-1/1A 631 m Agatdal+Vaigat Core logs Atane Atane Qilakitsoq Ravn Kløft Qilakitsoq Ravn Kløft+Kingittoq GK GANK-1 364 m Kangilia+Vaigat - GRO GRO-3 - Itilli+Kangilia+ Well logs PK GT GANT-1 891 m Itilli+Kangilia - ItilliPingunnguup Kuua Anariartorfik An Ik GW GANW-1 199 m Vaigat Agatdal+Vaigat - Itilli Atane Anariartorfik Ikorfat Anariartorfik Ravn Kløft+Kingittoq Uk Ma Marraat-1 448 m Vaigat Well logs ItilliUkalersalik Anariartorfik Um Umiivik-1 1200 m Itilli+Kangilia - Greenland 20 km20 km 54°W 71 ° 70 °3 0' 70 °N 71 °3 0' N Svartenhuk 52°W Eastern limit of N uussuaq Basin Eastern limit of N uussuaq Basin Fig. 1. Geological map of the study area showing well and outcrop locations. Abbreviations of outcrop, well and fault names are explained to the right, where lithostratigraphic units occurring at outcrops and wells are also listed. © 2017 GEUS. Geological Survey of Denmark and Greenland Bulletin 38, 49–52 . Open access: www.geus.dk/publications/bull 5050 Lithology and distribution of relevant formations The Atane Formation is known from the eastern part of the Nuussuaq Basin east of the Kuugannguaq–Qunnilik fault, (KQ fault, Figs 1, 2). The formation is up to 800 m thick in individual outcrops and consists of delta deposits, which include laterally extensive sandstone sheets (Dam et al. 2009). The mudstone-dominated, marine Itilli Formation (Fig. 2) is known from northern and western Nuussuaq (west of the Ikorfat fault) and is more than 2.5 km thick (Sønder- holm & Dam 1998). The Umiivik Member crops out in northern Nuussuaq between the Ikorfat and the Itilli faults (Fig. 1), whereas the Anariartorfik Member crops out west of the KQ fault. The up to 438 m thick marine Kangilia Formation (Fig. 2) crops out on northern Nuussuaq between the Ikorfat and Itilli faults (Fig. 1) and has been drilled in the GANT-1 and GRO-3 wells. It has also been measured in an outcrop on southern Nuussuaq. Mudstones dominate in the outcrops while sandstones dominate in the wells. The Annertuneq Conglomerate Member mainly comprises conglomerates and sandstones (Dam et al. 2009). The sub-marine to marine Agatdal Formation (Fig. 2) is known from the Agatdal area on central Nuussuaq west of the Ikorfat fault as well as from the GRO-3 well west of the K–Q fault (Fig. 1). The formation is up to 148 m thick and consists of mudstones, sandstones and conglomerates (Dam et al. 2009). The volcanic Vaigat Formation (Fig. 2) is up to 1600 m thick in western Nuussuaq and northern Disko and in- creases to at least 5 km in thickness on Ubekendt Ejland (Larsen et al. 2016). The lower part of the formation is dominated by hyaloclastic breccias that are overlain by lava flows. Methods Ten wells and eight sedimentary outcrop successions locat- ed in the Nuussuaq Basin and described by Sønderholm & Dam (1998) and Dam et al. (2009) were analysed to quan- tify the sandstone component of the siliciclastic formations of the Nuussuaq Group. All sandstone intervals were de- fined as potential sandstone reservoirs and expressed as the cumulative sandstone thickness of a formation. Potential reservoir content was defined as the cumulative sandstone thickness divided by formation thickness. The cumulative sandstone thickness in outcrops and wells was estimated from sedimentological logs and core descriptions. Mud- stones and heteroliths were classified as non-reservoir lith- ologies and included in the term ‘shale’. In the uncored GRO-3 well, sandstone content was determined from wire-line logs and implies a shale content of 0–15%. Five wells containing volcanic successions of the WGBG were analysed to identify potential reservoir sections within the hyaloclastite successions. These were quantified as the cumulative thickness of hyaloclastite breccias. Lava flows were classified as non-reservoirs. Porosity–permeability trends were established for the GANE-1/1A, GANT-1 and Marraat-1 wells based on core analysis data. The porosity of the clastic formations in GRO-3 was calculated from the density wire-line log. Sandstones with porosities >10% are referred to as porous sandstones. A porosity log of the GANE-1/1A well was generated from gamma-ray and den- sity logs obtained from core scans. Maligât U pe rn iv ik N æ s Slibestensfjeldet Kome Atane Itilli Agatdal Vaigat Kangilia Eqalulik Atanikerluk WGBG Quikavsak N uu ss ua q G ro up A lb ia n Dan. Pa le oc en e U pp er C re ta ce ou s Lo w er C re ta ce - ou s Cen. Tur. Maas. Se la nd ia n Cam. San. Con. W el l O ut cr opSeries Stage Group Formation Member Skansen Ravn Kløft Kingittoq Qilakitsoq Aaffarsuaq Anaanaa Naujánguit Ordlingassoq Annertuneq Conglomerate Anariartorfik Umiivik Kussinerujuk Fig. 2. Lithostratigraphic scheme of the Nuussuaq Group and the low- ermost part of the West Greenland Basalt Group (WGBG). Members studied here are indicated to the far right. Modified from Dam et al. (2009). 0 100 200 300 400 500 C um ul at iv e sa nd st on e th ic kn es s (m ) 0 500 1000 1500 2000 Formation thickness (m) 10% sa ndston e 50 % sa nd sto ne 10 0% s an ds to ne 25% san dst one Agatdal Fm Kangilia Fm Itilli Fm Atane Fm Fig. 3. Formation thickness versus cumulative sandstone thickness, data from the analysed wells and outcrops in the Nuussuaq Basin. 51 Reservoir properties of formations con- taining potential hydrocarbon reservoirs Potential reservoirs were identified within sandstones of the Atane, Itilli, Kangilia, and Agatdal formations and hyaloclastite breccias of the Vaigat Formation (Fig. 2). The main reservoir parameters including cumulative reservoir thickness (CRT), potential reservoir content (PRC) and porosity–permeability data are summarised below, with details in the Electronic Supplement (ES). Atane Formation. CRT is in the range 26–360 m cor- responding to a PRC of 45–80% (Fig. 3 and ES). The res- ervoir quality is well developed in central Nuussuaq with sandstone porosities of 5‒25% (mean 17%) and air perme- abilities of 0.5‒150 mD (Appel & Joensen 2014). Itilli Formation. CRT is in the range 21–458 m corre- sponding to a PRC of 2–51% (Fig. 3 and ES). The relatively low content of potential sandstone reservoirs compared to the Atane, Kangilia and Agatdal formations reflects sig- nificant variations within and between the members of the Itilli Formation. In the GRO-3 well, the individual sand- stone units are up to 100 m thick and average porosity is 4%. Kangilia Formation. CRT is in the range 0–134 m cor- responding to a PRC of 0–72% indicating significant lat- eral variation in depositional environments (Fig. 3 and ES). In the mudstone-dominated successions, the Annertuneq Conglomerate Member constitutes a potential reservoir. In the GRO-3 well, porosities range between 5–17% (average 6%). Agatdal Formation. CRT is in the range 71–148 m cor- responding to a PRC of 50–67% (Fig. 3 and ES). Porosities of 6–21% and permeabilities up to 9 mD were measured in the GANE-1 well (Fig. 4), and in the GRO-3 well, an average formation porosity of 9% was assessed. Vaigat Formation. Several oil shows have been encoun- tered in the hyaloclastites and lava flows. Only the hya- loclastites seem to possess the necessary permeability to constitute a reservoir despite indications of lower average porosities (6%) than the lava flows (8%). For identical po- rosity values, the permeability is 30 times higher for the hya- loclastites compared to the lava flows (Fig. 4). The CRT of the hyaloclastites is in the range 80–671 m corresponding to a PRC of 84–100% (Fig. 2 and ES). Porosity–permeability relations of potential reservoirs The regional distribution of porosity and permeability in the Nuussuaq Basin deposits is poorly known due to the scarcity of core measurements or studies concerned with the effects of diagenesis on reservoir quality (Kierkegaard 1998). One relatively swift way of improving the porosity database is by using core scans to generate a porosity log (Pedersen et al. 2013). This is shown for the Agatdal For- mation in GANE-1/1A in Fig. 5. The core log-generated 0.01 0.1 1 10 100 A ir p er m ea bi lit y (m D ) 0 5 10 15 20 He porosity (%) Trend A Trend B Marraat-1 Wells Formations GANE-1/1A GANT-1 Agatdal Fm Vaigat Fm (lava flows) Kangilia Fm Vaigat Fm (hyaloclastite) Itilli Fm Oil Shows Gas Fig. 4. Helium porosity and air permeability for selected wells. Oil shows are abundant along trend A (hyaloclastite reservoirs). Both oil and gas shows occur in the lava f lows (trend B). The siliciclastic samples generally plot between the two trends. Oil Gas 600 650 700 Depth (m) Porosity (%) Air permeability (mD) Core gamma ray (API) 0 5 10 10 0 200 400 600 80010.10.012015 Sandstone Shale Intrusive rock Core analysis Core log-porosity Core gamma ray GANE-1/1A GANE-1 GANE-1A LithologyShowsCore and log measurements, Agatdal Fm Fig. 5. Stratigraphical variation of lithology, porosity and permeability within the Agatdal Formation in the GANE-1/1A well. 5252 porosity curve fits nicely with the core measurements and the core log-derived lithology corresponds well with the lithological log from Dam et al. (2009). Core analysis data from the Marraat-1, GANE-1/1A, and GANT-1 wells were used to outline porosity–perme- ability trends within the siliciclastic and volcanic succes- sions (Fig. 4). In the siliciclastic reservoirs, the porosity and permeability data show a high degree of scatter and no con- sistent trend can be identified. The large range in poros- ity and permeability values probably reflects variations in grain size and diagenesis. A large part of the porosity in the GANT-1 sandstones is secondary and related to dissolution of detrital feldspar grains (Kierkegaard 1998). The hyaloclastite samples show a relatively high perme- ability–porosity ratio (trend A in Fig. 4) compared to the lava flows (trend B in Fig. 4). At 10% porosity, the expected permeability is 5 mD for hyaloclastites, but only 0.8 mD for lava flows, a tendency assumed to reflect textural con- trol on permeability. In hyaloclastites, a network of con- nected pores ensures fluid or gas flow, whereas the isolated pore systems in lava flows strongly impede permeability, even at high porosity. Conclusions The onshore Nuussuaq Basin in West Greenland contains potential hydrocarbon reservoirs within the siliciclastic Atane, Itilli, Kangilia and Agatdal formations, and within the hyaloclastite intervals of the Vaigat Formation. The si- liciclastic reservoirs occur in a wide range of geological en- vironments from fluvial over deltaic to slope and marine settings. The potential reservoir sandstone content is gen- erally more than 50% for the sections studied from the Atane, Kangilia and Agatdal formations, but significantly lower in the Itilli Formation. The cumulative sandstone thickness is mostly >100 m for all formations, including the Itilli Formation. Porosity and permeability data suggest that sandstone and hyaloclastite reservoirs may be of good quality with porosities up to 20%. Permeabilities are mostly below 10 mD. However, porosity and permeability data are restricted to the western part of Nuussuaq and the diagenetic control on the reservoir quality is poorly understood regionally. Acknowledgements This contribution is partly the result of a project funded by the Ministry of Mineral Resources, Greenland. References Appel, A.U. & Joensen, I.Á. 2014: Prograderende deltaaf lejringer fra øvre Kridt, Atane Formationen, Nuussuaqbassinet, centrale Vest- grønland. Unpublished Bachelor thesis, Department of Geosciences and Natural Resource Management, University of Copenhagen, 49 pp. Dam, G., Pedersen, G.K., Sønderholm, M., Midtgaard, H., Larsen, L.M., Nøhr-Hansen, H. & Pedersen, A.K. 2009: Lithostratigraphy of the Cretaceous–Paleocene Nuussuaq Group, Nuussuaq Basin, West Greenland. Geological Survey of Denmark and Greenland Bulletin 19, 171 pp. Kierkegaard, T. 1998: Diagenesis and reservoir properties of Campa- nian – Paleocene sandstones in the GANT#1 well, western Nuussuaq, central West Greenland. Geology of Greenland Survey Bulletin 180, 31–34. Larsen, L.M., Pedersen, A.K., Tegner, C., Duncan, R.A., Hald, N. & Larsen, J.G. 2016: Age of Tertiary volcanic rocks on the West Green- land continental margin: volcanic evolution and event correlation to other parts of the North Atlantic Igneous Province. Geological Maga- zine 153(3), 487–511. Oakey, G.N. & Chalmers, J.A. 2012: A new model for the Paleogene motion of Greenland relative to North America: Plate reconstruc- tion of the Davis Strait and Nares Strait regions between Canada and Greenland. Journal of Geophysical Research 117, 1–28. Pedersen, G.K., Schovsbo, N.H. & Nøhr-Hansen, H. 2013: Calibra- tion of spectral gamma-ray logs to deltaic sedimentary facies from the Cretaceous Atane Formation, Nuussuaq Basin, West Greenland. Geological Survey of Denmark and Greenland Bulletin 28, 65–68. Sønderholm, M. & Dam, G. 1998: Reservoir characterisation of western Nuussuaq, central West Greenland. Danmarks og Grønlands Geolo- giske Undersøgelse Rapport 1998/6, 36 pp. Sørensen, E.V., Hopper, J.R., Pedersen, G.K., Nøhr-Hansen, H., Guarni- eri, P., Pedersen, A.K. & Christiansen, F.G. 2016: Inversion structures as potential petroleum exploration targets on Nuussuaq and northern Disko, onshore West Greenland. Geological Survey of Denmark and Greenland Bulletin 38, 45–48. Authors’ address Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen, K, Denmark. E-mail: MLH@geus.dk