The Hegre Group – a complex stratigraphic interval: Example ......The Hegre Group – a complex...
Transcript of The Hegre Group – a complex stratigraphic interval: Example ......The Hegre Group – a complex...
-
The Hegre Group – a complex stratigraphic interval: Example from the Greater Sleipner AreaAnna Kulikova, Andreas Rittersbacher, Silvan Hoth, James Elgenes, Signe Ottesen and Annika Therese Ulfsdotter Heggheim
20 June 20Classification: Open
© Statoil ASA
-
Stratigraphy challenge
20 June 20172 Classification: Open © Statoil ASA
-
Salt tectonics
Permian fault blocks (Signe Ottesen, 2001) Top Zechstein -Top Sleipner Fm thickness map
15 km
15 km
20 June 20173 Classification: Open © Statoil ASA
-
Objectives of the study• Enhance the understanding of the deposition of a Triassic reservoir in
the Sleipner Area
• Enhance the decision making for potential Triassic exploration projects
Location and stratigraphy of the Sleipner Area
20 June 20174 Classification: Open © Statoil ASA
-
Facies from core: Proximal-medial part of a fluvial system
Cross bedding
Rip-up clasts
Erosional bases
Amalgamated channel fill deposits and paleosols
Paleosols with caliche
Cross bedding
Channel fill deposits
20 June 20175 Classification: Open © Statoil ASA
-
Facies from core: Distal alluvial plain
• A lot of mica –ponding, low energy
Terminal splay/ lake deltaAlluvial plain / ephemeral lake
• Gradationalboundaries
• Unconfined flow
Similar to examples of Smith Bank in UK sector (McKie, 2014)
• Parallel lamination
• Wave ripple & horizontallamination
• Roots, burrows
• Mudcracks and rip-up clasts
• Quiet setting
20 June 20176 Classification: Open © Statoil ASA
-
Facies modelDistal dry alluvial plain, terminal splays, lakes
• Unconfined flows from terminal splays
• Standing bodies of water - ephemeral lakes / ponds
• Aeolian?
Proximal to medial part of a fluvial system
• Channelized flow, maximum reworking
• Amalgamated sandstones, floodplain is
reworked and transported downstream
Cain & Mountney, 2009
20 June 20177 Classification: Open © Statoil ASA
-
Transport direction
Likely towards East / Southeast
Possible source from the Utsira High
Paleogeography is taken from McKie (2012) Figure 19a. Sediment dispersal is taken from McKie and Williams (2009). Active faults are taken from the Millennium Atlas (2003)
20 June 20178 Classification: Open © Statoil ASA
-
Intra Triassic lithological packages
• Heterogeneous
• Sandy
• Transitional
• Fine-grained (Smith Bank)
• Lack of biostratigraphic data
• Lithostratigraphic correlation
20 June 20179 Classification: Open © Statoil ASA
-
Combinations that occur at Sleipner Eastrare
Uncertainand rare
GRP1_3
P1_2
P1a/P1 P1
P1a
P1_3
P1_2
P1
P1a
P1_2
P1
P1a P1a
• If succession of identified packages is depositional and correct:
• Progradation of fluvial system has occurred
• Erosion could be an important factor in preservation of sandstones of the upper packages
• As packages are similar and thick –the fluvial system covered a large area and was flowing without restrictions.
rare
• Heterogeneous
• Sandy
• Transitional
• Fine-grained (Smith Bank)
20 June 201710 Classification: Open © Statoil ASA
-
Accommodation vs Sediment supply
Sandy amalagmated package
Transitional package
Fine grained package
• Progradation of the fluvial system• Decrease in subsidence rate or
increase in sediment supply or a combination of both
• NOTE that lateral change in facies could occur due to proximal to distal variations
Banham & Mountney, 2013
20 June 201711 Classification: Open © Statoil ASA
-
Evidence of erosion at the top of Triassic succession• Assuming that succession of lithological packages
is depositional and correct
• Different uppermost packages are missing in a number of the wells
• Unconformities have been observed at the top Triassic from dipmeter data
• Unconformities are also observed on seismic data
mis
sing
Dip
met
er d
ata
mis
sing
Dip
met
erda
ta
• Heterogeneous
• Sandy
• Transitional
• Fine-grained
20 June 201712 Classification: Open © Statoil ASA
-
1
Correlation and seismic section lines
5 km
20 June 201713 Classification: Open © Statoil ASA
-
trans
het/sandy
fine
trans
Well Correlation Line 1
On flanks ofan elevated pod
On top of the pod
1 2
3
• Sandy/heterogeneous
• Transitional
• Fine-grainedfines
4 5 6
20 June 201714 Classification: Open © Statoil ASA
-
Both wells drilled on flanks encountered
Skagerrak sandstones
Smith Bank
Older Skagerrakinterval is preserved
Jurassic Wedge, Active faultingLittle effect of
Jurassic erosion
Seismic section Line 1
BCUSkaggerakBase CoalSmith Bank (modelled)
• Sandy Skagerrak package is missing on top of the mini-basins and present on the flanks
• Faulting played a role as well
Skagerrak
2.5 km
1
2 34 6
No Skagerrak
Partly preservedSkagerraksuccession
20 June 201715 Classification: Open © Statoil ASA
-
Salt sediment interaction model
Sleipner Field example
2 3 4
SkagerrakSkagerrak
SALT
Smith Bank
1. Smith Bank – increased thickness in salt mini-basins2. Deposition of Skagerrak across the area with potential
depocentres or differential preservation above salt crestal collapse structures
3. Aalenian unconformity (Jurassic erosion) – partly or fully removes Skagerrak sandstone package
6 or 11
4 326 or 11
Model modified from McKie, 2014
20 June 201719 Classification: Open © Statoil ASA
-
Conclusions for the Sleipner Area
• Skagerrak fluvial system was active across the whole area and progradedtowards SE during formation of crestal collapse structures
• Erosion removed parts of Skagerrak deposits from tops of the inverted salt mini-basins
• Skagerrak sandstone is mainly preserved on the flanks of the inverted salt mini-basins and in the depocentres between the mini-basins, and partly on the top of the mini-basins
• Salt - sediment interaction models by McKie (2012, 2014) allow for the welland seismic observations made in the Sleipner Area
• Correlation of lithostratigraphic packages in absence of biostratigraphic data seems to be plausible, but uncertainty on the chronostratigraphy remains
• Hegre Gp is complex stratigraphic interval affected by a combination offluvial system dynamics, salt movements and Jurassic erosion
20 June 201720 Classification: Open © Statoil ASA
-
This presentation, including the contents and arrangement of the contents of each individual page or the collection of the pages, are owned by Statoil. Copyright to all material including, but not limited to, written material, photographs, drawings, images, tables and data remains the property of Statoil. All rights reserved. Any other kind of use, reproduction, translation, adaption, arrangement, any other alteration, distribution or storage of this presentation, in whole or in part, without the prior written permission of Statoil is prohibited. The information contained in this presentation may not be accurate, up to date or applicable to the circumstances of any particular case, despite our efforts. Statoil cannot accept any liability for any inaccuracies or omissions.
Presentation title
The Hegre Group – a complex stratigraphic interval: Example from the Greater Sleipner Area
Presenters name/title, etcAnna [email protected]
www.statoil.com
© Statoil ASA
Questions?
The Hegre Group – a complex stratigraphic interval: Example from the Greater Sleipner AreaStratigraphy challengeSalt tectonicsObjectives of the studyFacies from core: Proximal-medial part of a fluvial systemFacies from core: Distal alluvial plainFacies modelTransport directionIntra Triassic lithological packagesCombinations that occur at Sleipner EastAccommodation vs Sediment supplyEvidence of erosion at the top of Triassic successionCorrelation and seismic section linesSlide Number 14Slide Number 15Salt sediment interaction modelConclusions for the Sleipner AreaSlide Number 21