Abstract Volume Stavanger, 19th – 20th April 2016

Organizing committee:

Atle Folkestad, Statoil

Nadine Mader Kayser, Maersk Oil

Bjørn Kåre Bryn, Centrica

Israel Polonio, Lundin Norway

Domenico Chiarella, PURE E&P Norway

Tone Mydland, NPD

Advances in siliciclastic and carbonate

sedimentology: concepts and case studies from

the Norwegian Continental Shelf

The workshop has been sponsored by

Organizing committee: Atle Folkestad (Statoil) Nadine Mader Kayser (Maersk) Bjørn Kåre Bryn (Centrica) Israel Polonio (Lundin) Domenico Chiarella (Pure E&P)

Advances in siliciclastic and carbonate sedimentology: concepts and

case studies from the Norwegian Continental Shelf Valhall, NPD in Stavanger, 19th-20th April 2016

19th April

08:00 Registration and coffee

08:30 Welcome: Atle Folkestad (Statoil)

09:00 Keynote speaker – McKie, T.. (Shell UK E&P) - Triassic dryland fluvial reservoirs: palaeogeographic evolution, facies and reservoir behaviour

09:45 Orre, L. (Statoil) – The Triassic Lomvi Formation in the northern North Sea – depositional environment in a syn- to post-rift setting

10:15 Mouritzen, C. (Maersk Oil - UK) - The HP/HT Culzean Discovery: An Integrated Stratigraphic Approach for the Triassic

10:45 Coffee/Tea break

Chairs: Israel Polonio (Lundin) and Nadine Mader Kayser (Maersk)

11:00 Longhitano, S. (Univ. Basilicata) & Chiarella, D. (Pure E&P) – Sedimentation in tectonically-confined narrow basins: do classical depositional models still work?

11:30 Sømme, T. (Statoil) – Source-to-sink in exploration; examples from the Norwegian margin

12:00 Lunch break

Chairs: Domenico Chiarella (PURE E&P) and Bjørn Kåre Bryn (Centrica)

13:00 Messina, C. (Statoil) & Nemec, W. (UiB) - Facies anatomy and heterogeneity of a shallow-marine sandstone reservoir: the Mid-Jurassic Garn Fm in the Kristin Field, Norway

13:30 Kvernes, S. and Singh, V. (Statoil) – Visund Field: Pre- and syn-tectonic effect on the Brent and Viking Group

14:00 Jones, G. (VNG Norge) – Submarine fan conglomerates of the Upper Jurassic Melke Formation, Southern Halten Terrace

14:30 Charnock, M. (Lundin) – Jurassic sequence stratigraphy and the importance of bounding surfaces and unconformities, Johan Sverdrup area

14:50 Bruhn, R. & Waite, S. (Dong E&P) – Dude, where’s my shoreface? Reservoir prediction in the Late Jurassic transgressive nearshore deposits of the Heno/Ula Fm, southern North Sea

15:10 Coffee/Tea break

CORE SESSION - Bjørn Kåre Bryn (Centrica) and Nadine Mader Kayser (Maersk)

15:25 Open core session – General description and main characters

15:55 Restricted core session – Sedimentological discussion

Charnock, M. (Lundin) – wells 16/2-16 AT2, 16/3-8S (Johan Sverdrup) and 16/2-20 (Torvastad)

Bruhn, R. and Waite, S. (Dong E&P) well 2/12-1 (Mjølner) and 2/12-2S

17:00 End of day one

19:00 Dinner at De Røde Sjøhus

Organizing committee: Atle Folkestad (Statoil) Nadine Mader Kayser (Maersk) Bjørn Kåre Bryn (Centrica) Israel Polonio (Lundin) Domenico Chiarella (Pure E&P)

Advances in siliciclastic and carbonate sedimentology: concepts and

case studies from the Norwegian Continental Shelf Valhall, NPD in Stavanger, 19th-20th April 2016

20th April

08:30 Coffee/Tea

Chairs: Israel Polonio (Lundin) and Domenico Chiarella (PURE E&P)

09:00 Keynote speaker Pomar, L. (Univ. Baleari Islands - Spain) - Why do Carbonates Systems buck the trends of Sequence Stratigraphic Models?

09:45 Keynote speaker Tucker, M.E. (Univ. Bristol - UK) - Marine Permian of western Europe: beautiful rocks, remarkable stories and stratigraphy

10:30 Coffee/Tea break

Chairs: Nadine Mader Kayser (Maersk) and Atle Folkestad (Statoil)

10:45 Keynote speaker Wright, P. (PW Carbonate Geoscience) - Hypogene Palaeokarst and Burial Corrosion

11:30 Eliassen, A. (Statoil) - Carbonates, Spistbergen, A large Paleozoic evaporate karst system on Spitsbergen – an analog to the Paleozoic plays in the Barents Sea

12:00 Lunch break

Chairs: Israel Polonio (Lundin) and Bjørn Kåre Bryn (Centrica) 13:00 Ahlborn, M. (Dong E&P) - The Fafner Succession of the Lower Permian Gipsdalen Group -

possibilities in interbedded carbonates and evaporites in the southwestern Barents Sea

13:30 Dustira, A. (Statoil) - The role of depositional setting in spiculite reservoir development: analogues from Svalbard (Tempelfjorden Group)

14:00 Klausen, T. (UiB) - Facies distribution and detrital zircon signatures of the Early to Middle Jurassic Stø Formation of the Barents Sea

14:30 Coffee/Tea break

14:45 Marin, D. (UiS) – New Lower Cretaceous stratigraphic framework for the SW Barents Sea and its implications for paleogeographic reconstructions

15:15 Grundvåg, S.-A. (UiT) - Towards a refined depositional model for the Lower Cretaceous in Svalbard and the northwestern Barents Shelf: implications for palaeogeographic reconstructions and onshore-offshore correlations

15:45 Folkestad, A. (Statoil) – Variation in stacking style of delta-estuary couplets in clinoforms, Eocene Central Basin of Spitsbergen

16:15 Wrap up and end of the workshop

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Triassic dryland fluvial systems and reservoirs

Tom McKie

Shell UK Exploration and Production, 1 Altens Farm Road, Nigg, Aberdeen AB12 3FY, UK tom.mckie@shell.com

Triassic dryland fluvial systems across NW Europe were dominantly endorheic in character and terminated in playa, aeolian dune, sabkha or marsh settings. The large scale facies architecture of these systems was dominated by sand-rich, mobile channel belts which passed down palaeoflow over distances of 10’s to 100’s of km into progressively finer grained, smaller-scale channel systems before ultimately terminating due to loss of discharge. Fluctuating climate, possibly in response to volcanism, drove the expansion and contraction of these systems and resulted in a layered stratigraphy, particularly in medial to distal locations.

A variety of sandbody styles are present ranging from poorly connected ribbons to high net:gross “tanks” of well-connected channel belts. As a result of the erratic, seasonal discharge regime during deposition the heterogeneity within these deposits is complex. A variety of mud-prone baffles and barriers are commonly present, combined with a permeability structure dominated by very variable grain-size and cementation by groundwater carbonate. The reservoirs consequently vary in their dynamic behaviour over a range of timescales from short-term tests to long term production, with uneven fluid movement that can be difficult to predict.

Stratigraphic compartmentalisation is common. Extensive floodbasin packages, especially those associated with a major adjustment in the fluvial system, are obvious culprits. However, compartmentalisation can also result from the presence of bar-top fines draping large accretionary bar complexes, particularly when these approach the scale of individual fault compartments or small fields. This can be accompanied by relatively good lateral connectivity within the associated bar elements, leading to a layered, sheet-like behaviour. Abundant internal drapes may give the impression of lateral boundaries from well tests, leading to an interpretation of narrow sandbodies. Ribbon bodies are typically associated with small, avulsive channel systems in more distal settings. Flow in such facies may be generally poor due to a fine grain size and low connectivity, or may be briefly dominated by a subset of ribbon clusters which have fortuitously higher 3D connectivity.

Initial flow in large channel belt reservoirs is dominated by higher permeability, coarse-grained thalweg and lower bar deposits, which may show up as negative skin on well tests. If the coarse elements are extensive and amalgamated they can form high permeability conduits which, in conjunction with bar top fines, may encourage fluid over- and/or under-runs. Under depletion drive these conduits will deplete relatively quickly (depending on their extent and connectivity), but will also provide networks through the reservoir to drain lower quality upper bar and overbank sandbodies. The geometry and grain size of the lower bar and thalweg bodies decreases down-palaeoflow, ultimately becoming disconnected and losing their permeability contrast with the upper bar and splay facies. This can leave reservoirs with apparently reasonable sand:shale ratios that lack the permeability to achieve economic flow rates.

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Sedimentology of the Middle Triassic Lomvi Formation of the northern North Sea: depositional environments in a late syn-rift to post rift setting

L.T.E. Orre and Atle Folkestad

Statoil ASA

The Middle Triassic Lomvi Formation in the northern North Sea has been examined with the objectives to interpret the depositional palaeoenvironments and view this in the geological setting of the basin in terms of facies distribution. The dataset consisted of slabbed core and thin sections from three wells where the Lomvi Formation was encountered in the northern North Sea. Electrical logs from eight wells were used in addition to interpret the depositional environments.

Detailed analysis of the core samples indicates three main facies assemblages, representing aeolian, lacustrine and lake deltaic sedimentary environments. Deposits interpreted as aeolian are whitish grey to reddish brown, very fine- to medium-grained sandstones, mainly massive sandstones (structureless). Freshwater bioturbation occur in a few intervals where weakly developed parallel stratification can be seen. The roundness of the sand grains and the grain-size composition derived from thin sections suggest an aeolian origin in an intra-cratonic basin for these deposits. The interpreted lacustrine deposits consist of horizontally-laminated mudstones and siltstones intercalated with ripple cross-laminated and structureless siltstones. Bioturbation and desiccation cracks are observed. The interpreted lacustrine deltaic deposits are very fine- to medium-grained sandstones showing cross-stratification, ripple cross-lamination and freshwater bioturbation. The electrical logs were used to interpret non-cored intervals of the Lomvi Formation in order to assess the actual stratigraphic thicknesses and spatial distribution of these sedimentary facies associations. The aeolian and fluvial deposits appear to be widespread, whereas the lateral extent of lacustrine and deltaic deposits seems to be restricted.

The Lomvi Formation was deposited right after the Permo-Triassic syn-rift phase and the basin at that time had inherited the remnant of the Permo-Triassic rift-topography. The suggested depositional model takes this into account and suggests that this topography affected the facies distribution. Lacustrine, deltaic and alluvial-fan deposits were apparently confined to hanging-wall areas, whereas aeolian and fluvial deposits were associated with footwall areas.

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The HPHT Culzean Discovery: An Integrated Stratigraphic Approach for the Triassic

C. Mouritzen

Maersk Oil UK

The HPHT Culzean discovery is located in block 22/25a in the UK Central North Sea between the Lomond Deep and the Heron HPHT Cluster. The accumulation was discovered in 2009 by the 22/25a-9Z well. Subsequent exploration and appraisal wells 22/25a-10 and 22/25a-10Z were drilled in 2010, followed by 22/25a-10Y and 22/25a-11 in 2011. The primary reservoir is the Triassic Skagerrak Formation with a secondary reservoir in the Middle Jurassic Pentland Formation. The main reservoir is located at a depth of approximately 14,000 ft with a formation temperature of 175 DegC and a formation pressure of 13,575 psi, which is equivalent to an overpressure of 6,500 psi. A lean gas condensate column of 1,850 ft has been identified and the total recoverable reserves are estimated to be 250-300 MMBoe.

One of the principal challenges concerning the Skagerrak reservoir in Culzean is the stratigraphy and how it relates to the adjacent Quad 22 areas. Historically biostratigraphic age dating of the Skagerrak Formation in Quad 22 has been unsuccessful, unlike Quad 30 where ages are well-established and biostratigraphic recovery is good. Following the discovery well 22/25a-9Z however, it was possible to establish reliable ages for the Skagerrak Formation in Culzean. Based on these successful age dating results a regional integrated stratigraphic study was carried out on selected wells from Culzean and the adjacent Heron, Egret, Skua and Marnock fields. Several stratigraphic techniques (core sedimentology, biostratigraphy, chemostratigraphy and heavy mineral stratigraphy) were applied to the study wells. Not all techniques were equally applicable, but through interpretation and integration of the various techniques a heavy minerals zonation scheme has been established for the Triassic in the Culzean area and in particular for the Skagerrak Formation enabling the differentiation between the two main sandstone Members; Judy and Joanne.

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Sedimentation in tectonically-confined narrow basins: do classical depositional models still work?

Sergio G. Longhitano1 and Domenico Chiarella2

1University of Basilicata, Department of Science, Potenza, Italy – sergio.longhitano@unibas.it 2Pure E&P Norway AS, Oslo, Norway – domenico.chiarella@pure-ep.no

The effect of the tectonic control in the sedimentary basins often results in the development of specific marine depositional settings, including mini- or sub-basins, block-faulted embayments or narrow passageways. Oceanographic forcing factors, such as waves, currents and tides having influence on such atypical depositional sectors, can generate unexpected sediment routes or depositional mechanisms. In these types of basins, palaeogeographic reconstructions and depositional system identification are often problematic, because conditions for sedimentation can departs substantially from ‘rule-based’ classical depositional models (i.e., deltas, shorefaces, turbidites, etc.). Uncertainties can be reduced by comparison with appropriate outcrop analogues that recorded similar geological histories and depositional settings, although in different ages.

We present three main field-based case studies deriving from the analysis of some Neogene-to-Quaternary successions of southern Italy. The exposed sedimentary deposits belong to different tectono-stratigraphic settings and record marginal-marine, shelf and deep-water subtidal environments.

At the exposed forefront of the southern Appenine Orogen (Basilicata), mixed silici-/bioclastic sandstone deposits accumulated during the early Pleistocene, filling thrust-top depocentres elongated parallel to the main faults. In these settings, sedimentation was mainly controlled by waves in a shoreface setting, but also tides were able to provide a certain influence due to the funneling of many of these embayments. Owing to the low tectonic subsidence of these mini-basins, the coastal sublittoral systems built only their shallowest environments (i.e. shoreface topset), with no relevant foreset slopes or bottomset fines, resulting in wedge-shaped sandbodies deprived of more distal and deeper prosecutions.

The second case study is the Gorgoglione Basin, which is known to represent a middle-upper Miocene thrust-top elongate depression, filled by <3,000-m-thick deep-marine turbiditic sandstones. These spectacularly-exposed deposits show lateral and vertical abrupt transits from channel to lobe sandstones, revealing internal patterns that recorded the interplay between sediment volume compensations, relative sea-level changes and basin-scale tectonic pulses. Due to the unusual narrowing of the basin, the turbidite systems markedly differs from the classical, ‘shelf-slope-basin’ depositional models, suggesting the occurrence of important by-pass sectors of the basin and the direct transfer of huge volume of sediments from the delta front areas down to the deep-marine depocentres.

The third outcrop analogue is based on the observation of some ancient marine tidal straits, recently documented from the lower Pleistocene of Calabria. These tectonic-controlled corridors generated conditions for convergence of tidal currents across narrow passageways, resulting in tidal amplification and accumulation of thick (>100 m) successions of cross-stratified sandstones. These sequences exhibit specific lateral and vertical stratigraphic transitions to fine- or coarse-grained lithofacies, often revealing unexpected lateral passages

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to river deltas, aprons or fault-blocked substrates with singular features and facies distribution.

The reconstruction of the depositional conditions in such basins demonstrates how marginal- to deep-water systems changed their depositional features, as well as their stratigraphic stacking patterns and sedimentological attributes, as they were forced by structurally-induced thresholds, constrictions or specific basin configurations. These three outcrop examples thus represent depositional scenarios recurrent in extensional and contractional settings, but including sub-seismic-scale elements of unpredictable features that, if properly characterized in outcrop, can reveal new perspectives in the sedimentological modeling.

Figure 1. Outcrop examples of deposits accumulated in tectonically-confined narrow basins (southern Italy). From top to base: Shallow marine mixed siliciclastic-bioclastic deposits (Acerenza – Lucanian Apennine); Gorgoglione Flysh (Pietrapertosa, Lucanian Apennine); Tidal-strait mixed siliciclastic-bioclastic deposits (Catanzaro Strait - Calabrian Arc).

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Source-to-sink in exploration – examples from the Norwegian margin

Tor O. Sømme

Statoil ASA – tooso@statoil.com

Source-to-sink evaluation has become an important element in prospectivity assessment. As basins and provinces become more and more mature with respect to exploration focus, the industry is forced to go wider and deeper in order to mature new play concepts in areas that are less understood and which often suffer from lower seismic data quality. Success thus requires integrated models that link margin evolution and deposition of reservoirs, source rocks and seals. Source-to-sink thinking targets this need by linking tectonic evolution to landscape and seascape morphologies, and to sediment routing from onshore to offshore. Here we will discuss source-to-sink assessment in the Norwegian continental margin at three different scales: regional scale, marginal scale, and basinal scale. On the regional scale, break-up between Norway and Greenland set up structural asymmetry that has largely affected sediment routing into the North Atlantic ever since, and old basement weakness zones inherited from the Caledonian collapse have played a major role controlling onshore drainage throughout the Phanerozoic. On a marginal scale, structural inheritance and paleo-topography has controlled sediment generation and routing from the Norwegian mainland, and sediment budget calculations links changes in basin deposition to long-term landscape evolution. Finally, on a basin scale, the direct input locations of sand to the Late Cretaceous deep-water basins was linked to structural grain and old, inherited topography. Pulses of tectonic reactivation of a low-relief Late Cretaceous landscape resulted in discrete pulses of sand being delivered to the deep-water basins. Source-to-sink analysis at these various scales has implications for exploration in terms of reservoir distribution and quality, trapping, seal and source rock development.

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Facies anatomy and heterogeneity of a shallow-marine sandstone reservoir: the Mid-Jurassic Garn Fm in the Kristin Field, Norway

Carlo Messina1 and Wojciech Nemec2

1Statoil Research & Technology, 1364 Fornebu, Norway 2Department of Earth Science, University of Bergen

The Garn Formation of Halten Terrace, Norwegian Continental Shelf, has long been recognised as a gas and condensate-bearing succession of shallow-marine arenitic sandstones deposited by early syntectonic sedimentation during Jurassic rifting. However, the origin and spatial architecture of this formation remained unclear and rather controversial, which also led to simplistic models of reservoir heterogeneity. The present study from the Kristin Field indicates that the sand was deposited in an actively subsiding graben within the Jurassic seaway that linked the Boreal and Tethys open seas. Deposition involved repetitive cycles of tide-dominated to wave-dominated sedimentation, attributed to subsidence-driven relative sea-level changes. Sedimentation involved the development of tidal sand ridges, with episodic storm influence and a concurrent accumulation of sand in inter-ridge swales. Fairweather wave action with ridge erosion and sand bypass prevailed once accommodation became filled by sea floor aggradation, until a new increase in accommodation occurred due to tectonic subsidence. The transgressive-regressive cycles formed a transgressive parasequence set ~ 100 m thick. The suggested facies anatomy has important implications for reservoir heterogeneity, with the tidal sandstone ridges as a main architectural element. These semi-isolated sandstone bodies consist of dune cross-strata sets that form highly anisotropic reservoir mini-compartments. The two types of anisotropy are considered to be the main source of reservoir heterogeneity and a probable cause of the rapid pressure decline and low gas recovery in the Kristin Field. As an improvement for reservoir model, the dimensions of the sandstone ridges are estimated and a statistical approach is used to estimate the frequency distribution of cross-set volumes from the measured cross-set thicknesses. The estimates allow these sandstone bodies in the reservoir model to be populated with realistic percentages of cross-set volumes. The new heterogeneity model may facilitate more reliable simulation of condensate flow and a better assessment of gas recovery efficiency.

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Visund Field: Pre- and syn-tectonic effect on the Brent and the Viking Group stratigraphy

Sissel Kvernes, Vaibhava Singh, Håkon E. Eliassen

Visund PETEC, Statoil ASA

The Visund Field lies in block 34/8 and is located on the crest of the easternmost fault block, forming the north-western margin of the Viking Graben.

The Brent Group shows significant thinning going east on the fault block. Viking sediments of Berriasian age are observed over most of the field, implying limited BCU erosion on Brent Group. Previously this was explained by structural thinning. However, a DeCo* deformation would affect the Brent stratigraphy. On Visund, new wells on the eastern flank do not show increase in deformation. Is the current conceptual model correct?

A study was conducted to understand fault movement and development of DeCo. Biostratigraphic analysis along W-E cross-sections (perpendicular to main fault direction) identified 3 important erosional surfaces. Minimal erosion was observed on hanging walls. Erosional surfaces observed on the crest are not easily identifiable in Visund cored wells as they are located downflank on the fault blocks. All current info (all wells, seismic etc.) is used to create paleogeographic maps.

Figure 1. Fault movement causes preservation of stratigraphy and development of local accommodation space (Green color: shale. Yellow and Orange: sands)

Timing of fault movement is critical for the preservation of stratigraphy. Age differences of the sediments preserved on each side of faults gives the relative timing of movement (Figure 1). Fault movement occurred, prior to and during deposition of the Tarbert Formation (Late Bajocian) causing pre-Tarbert erosion into Ness in the west and eroding most of Brent to the east. During deposition of Heather Formation (Bathonian - Oxfordian), a reduction in tectonic activity is observed followed by erosion of Heather Formation (10-20 mill year missing). Reactivation of faults during deposition of the Draupne Formation (Tithonian – Berriasian);

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Active faults with large throws are observed to the east of the fault block. Erosion of Draupne (BCU) caused 3-6 mill years of sediments to go missing.

This understanding reduces the significance of DeCo to explain structural setting, consequently impacting the understanding of the deposition of sands and their preservation potential and reservoir communication.

* DeCo – Degradation Complex

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Spatial and temporal distribution of coarse grained submarine fan deposits and their context within the syn-rift tectono-stratigraphic evolution of the Upper

Jurassic Spekk and Melke Formations, Southern Halten Terrace

George Jones

VNG Norge

The recent drilling program that targeted Upper Jurassic syn-rift deposits on the southern Halten Terrace has resulted in an extensive dataset that will contribute to our understanding of rift systems in terms of the tectono-stratigraphic development.

It is well understood that the Jurassic syn-rift sedimentary succession of the Halten Terrace is dominated by shelfal to basinal mud and siltstones of the Melke and Spekk Formations, with isolated coarse-clastic deposits. The spatial and temporal distribution of these coarse clastic deposits is, however complicated and rather poorly understood. The extensive coring program in the Pil and Bue wells and subsequent well data from the Boomerang wells in the PL 586 licence provide a rare, high-resolution window into the process regime and sediment transfer mechanisms that supplied and distributed sediment into a small hanging wall basin and that ultimately provided the reservoirs for both the Pil and Bue discoveries.

Close to 475 m of conventional core was taken in the Pil main, Pil side track and Bue wells. This extensive core dataset provided a unique opportunity for detailed facies trends, stacking patterns and process to be documented in the context of seismically defined geomorphological architecture. The relatively close spacing of the three wells not only allows for temporal changes to be observed but also allows for a degree of three dimensional facies control.

The syn-rift stratigraphy recorded in the Pil and Bue wells can be broadly divided into early, peak and late rift packages. The Bue well recordes both early and late rift intervals which consists of fine grained, well sorted basin floor turbidite deposits and coarse gained, poorly sorted shoreface deposits respectively. Although correlation to the two Pil wells is difficult due to poor biostratigraphic control, the peak rift sequence is considered to be absent in the Bue well. Both the Pil main well and side track were TD’d in what is considered to be time equivalent early rift basin floor turbidite deposits, however these intervals were not cored. Overlying the early rift is a thick peak rift sequence (in excess of 250 m thick in the two wells) which consists predominantly of coarse grained non-cohesive debris flows and high density turbidites. A time equivalent late rift shoreface to the one encountered in the Bue well was also penetrated in the Pil side track and consists of similar facies.

The Pil and Bue wells confirm the complicated spatial and temporal nature of coarse-clastics deposits along rifted basin margins but have provided an extensive dataset that will help to better understand the heterogeneities of such reservoirs and aid future exploration.

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Jurassic sequence stratigraphy and the importance of unconformities and bounding surfaces, Johan Sverdrup area

Michael Charnock

Lundin Norway

Not since the FORCE Utsira High meeting in June, 2012 that was organised after the Lundin Avaldsnes discovery well 16/2‐6 in 2010 and the subsequent Statoil Aldous Major South 16/2‐8 well have cores from the Jurassic siliclastic reservoir section been made available for general display at a FORCE meeting from the developing Johan Sverdrup Field (Norwegian North Sea blocks 16/2; 16/3 and 16/5). In the subsequent four years (2010‐2014), a total of 30 exploration and appraisal wells were drilled across the field by operators Statoil (PL265 and PL502) and Lundin (PL501) to define the reservoir geometry of his giant oil field which is currently in the first construction phase lead by Statoil Petroleum AS (NPD fact pages). Coring was a significant feature of this exploration and appraisal programme and with only two exceptions; all wells were cored to a significant degree. A staggering total of 1.8 km of core has been taken to‐date and excluding borehole 19 A, all wells are now either released or scheduled for release before the FORCE seminar workshop date.

Prior to the viewing a brief introduction is given to the three wells intended for core displayed.

Lundin well 16/2‐16 and the subsequent sidetrack 16AT2 wells were located to define the north‐eastern part of the field. Both boreholes were extensively cored but the 16AT2 has been chosen (96m of core) to demonstrate the diverse sedimentary facies of the Triassic to Jurassic succession. This cored borehole represents one of the most complete successions in the field penetrated to‐date, but despite this, the sequence is still punctuated by stratigraphic breaks (UNC) that are considered to be both sequence boundaries (SB) and transgressive surfaces (TS) in nature. These stratigraphic breaks are related to the Mid Jurassic doming and subsequent deflation phase and Late Jurassic rifting of Thompson (2016).

Lundin well 16/3‐8 S located on the Avaldsnes High, on the eastern part of the field is approximately 6.8 km south‐east of the 16/2‐16 well. In this well, 71m of core were taken to investigate the thickness and quality of the Draupne sandstone reservoir as well as the Permian Zechstein carbonates. The base Draupne Unconformity (UNC) can be seen to be more extensive than in the 16AT2 (late Jurassic rifting phase) and the Draupne sandstone rests directly on a Triassic fluviatile interval above Zechstein carbonates that are developed in response to Permo‐Triassic extension phases. The Lundin 16/2‐20S well (53m of core) drilled the Torvastad prospect to the north of the Johan Sverdrup Field on the eastern flank of the informal Haugaland High (southern Utsira High complex). In contrast this core shows that Upper Jurassic sandstones are absent due to bypass and or subsequent erosion and the Draupne succession is dominated by spiculites interbedded with mudstones of the highstand systems tract (HST) associated with a 'latest' Jurassic ‐ 'earliest' Cretaceous extension phase. The cores also show an Upper Jurassic condensed section (CS) and a maximum flooding interval (MFI). The maximum flooding is rarely seen as a surface but an interval of a few metres of basinal mudstones. Participants have also the opportunity to see the cored 'Base Cretaceous Unconformity' or in this case, its correlative conformity.

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The three cores chosen for display, therefore, illustrate a diverse sequence of sedimentary facies and a variety of correlative bounding surfaces. Their display is hoped to promote a good deal of interest and discussion.

Summary of Cores on display

16/2‐16 AT2, 16/3‐8 S (both Johan Sverdrup Field) and 16/2‐20 S (Torvastad)

Lithostratigraphic Groups on display

Cromer Knoll, Viking (primary focus), Vestland, Statfjord, Hegre and Zechstein Groups.

Notice

The FORCE organising committee depends on the goodwill of companies to provide interesting and relevant data to show at these meetings. In a corresponding spirit of cooperation, participants are kindly asked not to photograph the cores laid out on display during this meeting.

Acknowledgement

Lundin Norway wish to thank PL501 Partners Statoil Petroleum AS and Maersk Oil Norway AS for abstract approval (18.3.16) and for permission to show these cores at this FORCE meeting to promote discussions and advances in siliclastic sedimentology and sequence stratigraphy.

Reference

Thompson, E. (2016) The Structural Evolution of the Utsira High. FORCE Structural geology network seminar presentation. 15th March 2016.

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Dude, Where’s my shoreface? – Reservoir prediction in the Late Jurassic transgressive nearshore deposits of the Heno/Ula Fm., southern North Sea

Rikke Bruhn and Shaun Waite

Dong E&P Norway AS

The Mjølner field (PL113) is the northern extent of the structurally complex Mjølner-Gert Ridge, which straddles the NO-DK boundary in the North Sea and forms the boundary between the Feda Graben and the Heno Plateau. Oil was discovered in Kimmeridgian nearshore sandstones of the Gert Mb. (basal part of the Heno/Ula Fm.) in Gert-1 and in 2/12-1 Mjølner. All subsequent appraisal wells (Gert-2, -3, -4 and 2/12-2S) encountered highly variable reservoir thickness and quality, and only trace hydrocarbons. The understanding of facies variations (and possible associated permeability variations) is critical to evaluating the commercial potential of the discoveries. Seismic imaging of the reservoir interval is hampered by the great burial depth (4600-4900m), the exceedingly complicated structuration of the Mjølner-Gert Ridge, and the distribution of facies in the reservoir models therefore largely relies on conceptual depositional models.

The best reservoir facies in the Gert-1 and 2/12-1 Mjølner wells are interpreted as middle-upper shoreface. And so the question is – what sort of shoreface environment was it?

In a semi-regional context the Gert Mb. represent relatively low-energy coastal environments that backstepped across the Early-Middle Jurassic unconformity, from the tectonically confined Feda Graben and onto the Heno Plateau. The transgressed landscape was likely rugged due to subaerial erosion and syn-depositional faulting primarily along pre-Late Jurassic fault grains. As a result both sediment supply and accommodation space varied laterally resulting in highly heterogeneous nearshore environments. This heterogeneity was only partially compensated for by longshore transportation in a low wave-regime environment. The depositional environment is similar to Late Jurassic nearshore environments further North in the North Sea and Atlantic rift corridors and could be a relevant analogue to Intra-Melke and Rogn Fm. deposits in Mid Norway.

In this talk we will present our current understanding of the Late Jurassic tectonic evolution of the Mjølner area and discuss the possible implications for the evolution of depositional environments and resulting facies architecture in the fault-controlled transgressive environment.

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Why do Carbonates Systems buck the trends of Sequence Stratigraphic Models?

Luis Pomar

University of the Balearic Islands, Mallorca, Spain

It is a common practice to apply the sequence analysis methodology derived largely from siliciclastics to carbonate systems. Nevertheless, few of these approaches address the specifics of carbonate systems, and sometimes red and blue triangles are placed using the grain size trends or changes in sediment patterns, which, in carbonates, may or may not be meaningful. When analyzing carbonate systems, “the absence of rules” becomes the rule, and instead using the changes in biotic components to infer the sea-level trajectories can more accurately capture the specificity of each example.

In the analytical strategy for constructing a meaningful reservoir model, building a realistic depositional model is a prerequisite, but in carbonates these can be further refined. In carbonate systems, the process/product relationship is much more complex and diverse, with several feedbacks and responses that may or may not be linear. Moreover, there is no a unique and consistent response of the system to the changes in accommodation as this may be either be driven by changes in the physical space (physical accommodation) or by the building capacity (ecological accommodation) of the system. Also, bedding patterns and bounding surfaces alone may not be of much utility. Rock packages bounded by physical surfaces are better characterized by changes in relative sea level due to the depth dependence of many carbonate-producing organisms. Having this powerful tool, there seems no reason to remain wedded to analyzing the less reliable bounding surfaces.

In carbonates, genetic analysis (process-product relationship) carried out on the composition and preservation of the skeletal- and non-skeletal components has proven to be very useful procedure. It permits to more accurately determine the changes in paleobathymetry, reflecting changes in accommodation. “Eco-stratigraphy” is becoming very useful to interpret platform carbonates and predict the architecture and distribution of facies heterogeneities. It requires knowledge of basics of paleoecology, but it has the potential to become a fully predictive technique. The limits to this analytical strategy are set by the knowledge (or lack thereof) of the ecological requirements of the ancient biota. Its advantage is that, in all cases, it generates new questions that lead us to look for answers that, in turn, yield more realistic interpretations and enhanced predictions of lithofacies heterogeneities.

20

Marine Permian of western Europe: beautiful rocks, remarkable stories

Maurice Tucker

University of Bristol, Bristol BS8 1RJ, UK

The carbonate-evaporite Zechstein succession of NW Europe is a major hydrocarbon target with reservoir facies well-developed in shelf-margin oolitic grainstone and fractured slope wacke- mud- stone. Locally important reservoir rocks are breccia, the product of karstic or evaporite dissolution, and microbialite. Source rocks developed in restricted lagoons and within lower slope facies through photic-zone euxinia, although older (Devonian-Carboniferous) and younger (Jurassic) organic-rich facies also provided oil and gas. The Southern Permian Basin had similarities with the Mediterranean, although connection to the open ocean to the north (Panthalassa) was through a 2000 km long channel. Being an intracratonic basin, TST, HST and FSST carbonates deposited around the basin margin, controlled largely by eustatic sea-level changes and local tectonics, alternated with lowstand gypsum-anhydrite platforms and thick basin-fill halite units, disconnected from the open ocean. Diagenesis of the carbonates is commonly complex, involving reflux dolomitisation, limestone neomorphism, anhydritisation, dedolomitisation (early-burial-uplift), and collapse brecciation, largely the result of mineralogical changes and dissolution of interbedded evaporites. Although prediction of porosity is difficult, diagenesis does follow a predictable path. This talk will briefly review the Zechstein geology and present some new data and ideas concerning the stratigraphy, diagenesis, source-rock potential and nanoporosity, based on the spectacular outcrops of NE England and core material from across the SPB.

21

Hypogene Palaeokarst and Burial Corrosion

Paul Wright

PW Carbonate Geoscience

Porosity is lost with depth in sedimentary rocks and especially in limestones and dolomites, but is that always the case? There are now many examples of reservoir quality developing in carbonates at depth as a result of burial fluids (hypogene fluids), in some cases creating high porosities and permeabilities in previously tight carbonates. The effects range from microporosity to km-scale breccia pipes, and when macroporosity is produced the term hypogenic karst is used. Several processes capable of doing this have been known for some time although other mechanisms have more recently been proposed including pressure changes in the reservoirs in the Pre-Caspian and clay decomposition in the Pre-Salt reservoirs of the South Atlantic. Not all this dissolution takes place at depth and the fluids responsible, although sourced at depth can create porosity near surface, resembling meteoric palaeokarst.

What is critical is to identify the effects of these hypogene fluids correctly as often they are mistaken for other dissolution processes and linked to lowstand surfaces and unconformities. Criteria from seismic to core to pore scale will be reviewed and examples shown from a wide range of reservoirs. Both syn-depositional and tectonic fractures commonly provide the main conduits for the movement of these fluids but smaller scale features such as stylolites and related fractures are seen to commonly play a role in controlling reservoir quality.

22

A large Paleozoic evaporate karst system on Spitsbergen – an analog to the Paleozoic plays in the Barents Sea

Arild Eliassen

Statoil ASA – areli@statoil.com

Large volumes of carbonate breccia occur in the late syn-rift and early post-rift deposits of the Billefjorden Trough, Central Spitsbergen. Breccias are developed throughout the Moscovian Minkinfjellet Formation and in basal parts of the Kazimovian Wordiekammen Formation. Breccias can be divided into two categories: (i) thick, cross-cutting breccia-bodies up to 200 m thick that are associated with breccia pipes and large V-structures, and (ii) horizontal stratabound breccia beds interbedded with undeformed carbonateand siliciclastic rocks. The thick breccias occur in the central part of the basin, whereas the stratabound breccia beds have a much wider areal extent towards the basin margins. The breccias were formed by gravitational collapse into cavities formed by dissolution of evaporite beds in the Minkinfjellet Formation. Several dissolution fronts have been discovered, demonstrating the genetic relationship between dissolution of evaporites and brecciation. Textures and structures typical of collapse breccias such as inverse grading, a sharp flat base, breccia pipes (collapse dolines) and V-structures (cave roof collapse) are also observed. The breccias are cemented by calcite cements of pre-compaction, shallow burial origin. Primary fluid inclusions in the calcite are dominantly single phase containing fresh water, suggesting that breccia diagenesis occurred in meteoric waters prior todeep burial of the sediments.

The timing of gypsum dissolution and brecciation was most likely related to major intervals of exposure of the carbonate platform during Gzhelian and/or Asselian/Sakmarian times. These intervals of exposure occurred shortly after deposition of the brecciated units and before deep burial of the sediments.

Solution collapse breccias observed in the Minkinfjellet and Wordiekammen formation are analogous to large seismic scale karst features seen in the equivalent upper Cretaceous carbonate units in the Barents Sea. These karst modified carbonate units can act as highly prospective reservoirs in the still moderately explored Paleozoic plays in this region.

23

The Fafner Succession of the Lower Permian Gipsdalen Group - possibilities in interbedded carbonates and evaporites in the southwestern Barents Sea

Morten Ahlborn

DONG Energy, Norway

The uppermost part of the Gipsdalen Group represents a succession not yet fully understood or studied in the Norwegian Barents Sea. So far the succession is not penetrated by exploration wells but seismic analysis indicates a succession comprising interbedded evaporites and carbonates - and in basinal settings; anhydrite and halite. This underexplored succession opens two new plays in the Norwegian Barents Sea and will be presented for the first time in this presentation.

This study has mapped the 'Fafner Succession' in the entire Norwegian Barents Sea. It appears to be regionally widespread from the down-dip flank of the Loppa High in the West to the Tiddlybank Basin and Finnmark Platform in the East and South - except on structural highs where the characteristic strong amplitudes of the succession appears to be missing.

The top and base of the succession are defined by unconformities, and especially the top of the succession is interpreted to have formed as a consequence of karst overprint and dissolution. The high relief topography is especially evident proximal to structural highs and platform margins.

The Fafner Succession may form two interesting new plays in the Barents Sea; first karstified carbonates, encased in evaporites which may have formed on structural highs within the Fafner Succession itself . This concept resemble a very prolific play in the Persian Gulf (Late Neoproterozoic to Early Cambrian Ara Group (South Oman Salt Basin).

Secondly, a more widespread play using the evaporite-dominated Fafner Succession as the seal. Hypesaline brines from the Fafner Succession may have flushed the underlying carbonates of the Ørn Formation forming thick zones of dolomites as the reservoir. The effect of saline brine from the evaporitic Gipshuken Formation into the underlying carbonates of the Wordiekammen Formation are studied in detail on Svalbard and it is suggested that similar processes are likely to have happened elsewhere in the offshore Norwegian Barents Sea.

24

The role of depositional setting in spiculite reservoir development: analogues from Svalbard (Tempelfjorden Group)

Anna Dustira

Statoil ASA – adus@statoil.com

Extensive outcrops of the Tempelfjorden Group across Svalbard provide an excellent analogue to the roughly age-equivalent Tempelfjorden Group in the Barents Sea. With field studies on Svalbard as the basis, a depositional model for the Tempelfjorden Group is discussed, and the relationship between basin setting and distribution of potential reservoir units is examined.

The depositional model identifies depth-dependent facies associations reflecting inner, mid and outer shelf depositional zones. The inner shelf is characterized by well-sorted glauconitic sandstones and limestones reflecting nearshore sand flats, sandy shoals and coarser, bioclastic shell banks, reworked by tides, waves and periodic storm events. Biotic assemblages are fully heterozoan (brachiopods, echinoderms, bryozoans and siliceous sponges). Light-colored, nodular to massive, spiculitic cherts prevail across the mid-shelf, indicative of broad offshore plains populated by abundant siliceous sponges. Bryozoans and echinoderms may occur at the margin between the mid and outer ramp, forming local build-ups on slightly elevated areas; on Svalbard these do not appear as major reef-builders, compared to more distal settings in the Barents Sea (Bjarmeland Group). The outer shelf includes facies associations of dark, bedded to massive spiculitic cherts, silicified mudstones and black shales, formed by the accumulation of sponge spicules and fine-grained suspended matter under quiet-water conditions.

Qualitative assessment of reservoir potential of the Tempelfjorden Group facies on Svalbard suggests that in general, proximal facies have the greatest reservoir potential, with light-colored spiculites and glauconitic sandstones as the best candidates. Lateral facies variations across the Svalbard depositional basin are steered by basin morphology. While distal localities (central and western Spitsbergen basin depocenter) comprise mainly non-reservoir facies packages of dark spiculites and shales, proximal localities (NE Svalbard, shallow homoclinal ramp setting) show potential reservoir-quality units of mixed spiculite-sandstone with gross thicknesses of up to 40m.

25

Depositional history of a condensed shallow marine succession from the Lower to Middle Jurassic Stø Formation of the Barents Sea constrained by U-Pb detrital zircon

Tore Grane Klausen1, Reidar Müller2, Jiří Sláma1,3, William Helland-Hansen1

1University of Bergen, Department of Earth Science, Allégaten 41, 5007 Bergen, Norway 2Tullow Oil Plc, Tordenskioldsgate 6B, 0160 Oslo, Norway 3Present address: Institute of Geology CAS, v.v.i., Rozvojová 269, 165 00 Prague 6, Czech Republic

The Early to Middle Jurassic Stø Formation (Toarcian to Bathonian) was deposited in a relatively shallow (10s of meter deep) epicontinental sea in northwestern Pangea. It comprises a condensed, predominantly marginal marine succession characterised by long hiatuses and erosional reworking with several horizons of extraformational pebble grade conglomerate. These conglomerates are enigmatic since similar grain sizes are not found in the underlying strata, which is a likely sediment source for this condensed and reworked Jurassic succession. Detrital zircon age signatures were analysed in order to determine the origin of the coarse grains, in addition to a sedimentological study aimed at distinguishing between different types of conglomerates lags and the relative stratigraphic position of the samples.

13 core samples gathered from discrete facies association from different stratigraphic intervals throughout the formation at different locations in the basin were analysed for detrital zircon U-Pb ages. Results show that the Early to Middle Jurassic Norwegian Barents Sea was dominated by local, extrabasinal source areas such as the Caledonides in the south and southwest, a Fennoscandian source to the southeast, and erosion of underlying strata with Triassic zircon grains in northern parts of the basin.

By integrating sedimentological observations and provenance data, this study links stratigraphically and geographically offset deposits and show trends in the sediment routes within this condensed section. Conglomeratic horizons could not be correlated directly, they instead record influx from one or two of the southern provenance areas, characterised by either Caledonian or Fennoscandian age peaks, or a mix between three different sources. This shows that the influx of coarse grained material cannot be linked to a single event or source area, while at the same time proving extrabasinal sources to the south of the basin.

26

A new Lower Cretaceous stratigraphic framework for the SW Barents Sea and its implications for paleogeographic reconstructions

Marin Dora, Escalona Alejandro, Kasia K. Śliwińska

University of Stavanger - dora.l.restrepo@uis.no

Extensive seismic surveys and wells publically available from the Norwegian Petroleum Directorate database (Petrobank) were analyzed to define a sequence stratigraphic framework for the SW Barents Sea. The purpose of the present study is to improve the understanding of the basin fill, which was otherwise challenging by applying lithostratigraphic correlations only. Seven sequences (S0-S6) are now defined and age of sequences is established by dinocyst stratigraphy. Detailed seismic facies analysis is also perfomed and eight different seismic facies are interpreted including: wedges, mounds and lenses. Additionally, three different scales of clinoforms are described: clinoform sets with 40-100 m height, which are interpreted as deltaic/shoreline clinoforms; 2) clinoform sets with <150 m height, which represent sediments prograding in shallow waters; and 3) clinoforms with a height of >150 m, representing shelf-slope clinoforms.

Our interpretations suggest that S0 (Berriasian-?Valanginian) was well developed in the Hammerfest Basin, where in the northern part coarse-grain sediments were fed by multiple canyon sources from the Loppa High, forming a linear belt interpreted as coalescent fans. In contrast, sedimentation in the southern part was controlled by the Troms-Finnmark Fault Complex, forming mostly orthogonal slope deposits. The middle and eastern part of the basin were dominated by shallow marine environments, which were partially continental in periods of regression. In the Bjarmeland Platform this sequence correlates with the Klippfisk Formation. In S1 (Hauterivian-early Barremian) the configuration of the Hammerfest Basin remained similar to S0, but the input of coarse grain sediments decreased. In the Nordkapp Basin shelf-slope clinoforms that prograded to SW are identified. Those clinoforms are interpreted up to S6. During the deposition of S2 (late Barremian-early Aptian) and S3 (tentatively late Aptian) the eastern part and partially the central part of the Hammerfest Basin remained as a shallow marine basin. The rest of the basin is interpreted as deep marine with a narrow shelf in the northern and southern boundaries. Fine-grained mass transport complexes and deep marine heterolithics sediments usually affected by small-scale normal faults, became the dominant deposits in most of the basin, but localized coarse-grained input along the basin margins was interpreted. Clinoforms of different scales that prograded to the SW are mapped in the Bjarmeland Platform and in the Nordkapp Basin. In the western Bjarmeland Platform and the Fingerdjupet Subbasin, the clinoforms prograded to the SE. Within S4 (Albian) the SE part of the Loppa High become flooded, including the canyons that supplied sediments to previous sequences. At the same time, some wedges were identified in the southern flank of the Loppa High. The clinoforms in the western Bjarmeland Platform are observed neither in this nor younger sequences, but it can be due to later erosional events. Finally, during the deposition of S5-S6 (Albian to Cenomanian) the eastern part of the Loppa High was flooded and shelf-slope clinoforms are identified in a narrow area of the NE part of the Hammerfest Basin, showing a prograding margin.

27

Towards a refined depositional model for the Lower Cretaceous in Svalbard and the northwestern Barents Shelf: implications for palaeogeographic reconstructions and

onshore-offshore correlations

S.-A. Grundvåg1, D. Marin2, A. Escalona2, B. Kairanov2, H. Nøhr-Hansen3, K.K. Śliwińska3 M.E. Jelby4 & S. Olaussen5

1Department of Geology, UiT – The Arctic University of Norway, P.O. Box 6050 Langnes, 9037

Tromsø, Norway 2Department of Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway 3Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K

Denmark 4Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350

Copenhagen K, Denmark 5Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen,

Norway

Following several technical discoveries in the Lower Cretaceous succession on the Barents Shelf (e.g. Skalle and Salina), the interval is listed as a play model by the Norwegian Petroleum Directorate. However, the Lower Cretaceous palaeogeography and basin development on the Barents Shelf are not fully understood. Through detailed onshore sedimentological studies in combination with biostratigraphic analyses, seismic mapping and well ties offshore, this study provides new insights into the evolution of the Lower Cretaceous depositional system in the northwestern Barents Sea. In Svalbard the Lower Cretaceous strata consists of offshore shelf to paralic deposits of Valanginian to Albian age, and includes a lower Barremian subaerial unconformity. The unconformity formed in response to uplift associated with opening of the Amerasian Basin. The persistent areal extent of the unconformity suggests that large parts of the northern Barents Shelf were exposed. Biostratigraphic studies indicate that Barremian strata occur above and below the unconformity, indicating that the shelf was exposed for a limited amount of time (<2 million years). Due to southward tilting of the shelf, vast amount of eroded sediments were transported and deposited in basins south of Svalbard. The presence of the subaerial unconformity onshore Svalbard, onshore-measured southeastward sediment transport directions, as well as SE-directed clinoforms in the Bjarmeland and Fingerdjupet areas, suggest that the onshore and offshore strata were part of the same palaeo-drainage system. The clinoforms observed on the Barents Shelf are generally mudstone dominated. This relates to the hydrodynamic conditions in the receiving basin where frequent storm activity trapped sand-grade sediments in the inner shelf areas. This resulted in a net basinward transport of mud-grade sediments and the formation of a mud-prone subaqueous shelf-prism that was detached from its shoreline with a shelf-break located several tens to hundreds of kilometers further basinward. It is therefore suggested that the potential for reservoir-quality sandstones in the Lower Cretaceous clinoforms on the Barents Shelf is mostly limited to thin sheets in the clinoform topsets. The sandstone content in the clinoform slope and toe-sets is expected to be generally low.

28

Variation in stacking style of delta-estuary couplets and associated deep-marine fans; an example form the Eocene Central Basin of Spitsbergen

Atle Folkestad1, Erik P. Johannessen1, Ronald J. Steel2

1Statoil ASA 2University of Austin - Texas

The Eocene of the Central Basin of Spitsbergen shows a series of eastward building clinothems deposited in a foreland basin. This basin was formed by a westerly active fold and thrust-belt which also acted as provenance area for these shallow-marine sand-wedges. Some of these shallow-marine wedges prograded onto the shelf, whereas some of them reached the shelf-edge and have associated deep-marine sand-lobes.

Three of these clinothems have been studied with focus on depositional environment, lateral facies variations, internal stacking pattern and shoreline trajectory pattern. All of them show a regressive deltaic to transgressive estuary/tidal couplet. Internally, there are clear differences between the three clinothems in terms of the style of the regressive deltaic part and the transgressive estuary part. The deltaic parts range from a) fluvial and punctuated mass-flow style; b) wave reworked and delta front collapse style; and c) mixed tide and fluvial influenced delta. The transgressive parts of the clinothems show a variation of the thickness of estuary sandstones and coastal plain fines developments conditioned on the degree of aggradation.

Previous studies of these Eocene clinothems have interpreted the associated deep-marine sand-lobes as due to: a) sea-level fall with shelf-incision and basinward movement of the deltaic system beyond the shelf-break; b) high sediment-supply mechanism as hyperpycnal flow within shelf-edge deltas feeding the basin-fans during sustained flow; and c) having a narrow shelf that easily gets prograded across with high sediment supply.

On individual basis each of these clinothems can be interpreted with these mechanisms above. However, it is interesting to see how the shape and size of each clinothem has a direct effect on the next clinothem that occurs above. As a clinothem consist of a dominant muddy part, the mud-volume can be stored: at the shelf-edge and expand the width of the shelf, on the shelf and building up the shelf height or even be stored more landward within the lagoonal and coastal areas, starving the shelf.

This study show how a volumetrically-limited clinothem enables the next clinothem above, to easily cross the shelf and feed sediments down the shelf slope from a fluvial delta. The two following clinothem faced a wider shelf that first gave a wave-dominated delta and finally a mixed tidal and fluvial delta capped by an estuary.