The Permo-Triassic story of the
Sindbad/Sesam well (Nordland Ridge)
Thomas Tvedt, E.ON Exploration & Production Norge AS
FORCE seminar - Underexplored Plays
8-9th April, 2015
Presentation outline
Brief Introduction to the Permian and Triassic geology in the area
Introduction to the targets of the Sesam/Sindbad well
Triassic Sindbad amplitude anomaly observations
Sindbad modeling
Sindbad results
Permian Sesam depth prognosis
Sesam results
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The Permo-Triassic story of the Sindbad/Sesam well
(Nordland Ridge)
PL350: Awarded in 2004, Relinquished in 2012
Partners: E.ON E&P Norge AS (operator)
Statoil
PGNiG
E.ON E&P Norge AS drilled a Triassic and a Permian prospect in 2011/12 on
the Sør High of the Nordland Ridge in the Norwegian Sea. The intent was to
test an amplitude anomaly in the Triassic section Sindbad (6507/6-4S) on the
long path down to the Permian prospect Sesam (6507/6-4A).
Both wells were unfortunately dry but gave a better understanding of the
Triassic and Permian and shedding light on the need for higher resolution
data.
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Permian Palaeogeography
Warm water platform carbonates
Nordland Ridge & East Greenland
Organic rich source rock basins
Jameson Land & Helgeland Basin
Evidence of HC generation and migration
Fluid inclusions in exploration wells and outcrops
Shows in shallow research boreholes
Modified from Stemmerik 1997
Modified from Müller et al. 2005
Palaeogeographic Maps and Tectonics–
Griesbachian - RhätianPost-rift phase 3 (Norian-Rhätian) represents termination of the late Triassic tectonic event. Progradation of extensive fluvial system inthe end of this phase is related to an uplift of the Norwegian Mainland. Gradual increase in the humidity of the climate.
Idealised chronostratigraphy illustrates basin
fill history of the Mid-Norwegian shelf and
East Greenland
Expected reservoir unit in Sindbad
comprises part of Unit Tr5
Unit Tr5 is of Norian to Rhätian age-
Post rift phase 3
Lower boundary defined by the last
occurrence of thin evaporitic beds (Tr4)
before going into dominant continental
palyno-facies of Tr5.
Lower part of unit (>300m) is deposited in
shallow and extensive mud-dominated
lacustrine basin
Upper part of unit (Sindbad level) consists of
thick sandstones beds interbedded with
mudstone and thin coals
Upper part of Tr5 deposited in a fluvial
system dominated by moderate to high
sinuous channels
Tr5 unit represents an overall coarsening
upward trend from a mudstone-rich
lacustrine flood-basin to a sand-dominated
fluvial environment
Late Permian to Triassic Litho-Chronostratigraphy
Modified from Müller et al. 2005
Triassic Unit TR5 Sedimentology and
Depositional Environment
Tr5
Sesam & Sindbad
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Sesam
Sindbad
Sesam
Sindbad
Dolomite/Anhydrite
Biogenic gas
Grey Beds
Red Beds
Åre Fm
NW SE
Former PL350 in 6507/6
East of Skarv field
Saga well, 1986
(Sindbad)
(Sesam)
Depth surface of Top Permian
Depth surface of Top Sindbad with RMS amplitude overlain
TW
T
Seismic angle stacks
Near angle 5-15 degrees Far angle 25-35 degrees
NW SENW SE
Stronger amplitude response up-dip from the 6-1 well on both
nears and fars
Strong degradation of frequency content from near to far angle
11 -
Pre-stack offset gathers from 6507/6-1 to Sindbad
6507/6-16507/6-4SNW SE
Red is hard
Offset 200-3200m
Seabed
BCU
Sindbad level
Evaporite
35 55
12 -
Pre-stack angle gathers from 6507/6-1 to Sindbad6507/6-16507/6-4S
NW SERed is hard
Angles 5-41 degrees
BCU
Sindbad level
Evaporite
RMS maps on full offset seismic
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Data-room September 2010 Geoscience Dpt
3 km
Lower eventUpper event
Saga well, 1986
(Sindbad)
Saga well, 1986
(Sindbad)
Depth contours Depth contours
AVO modeled gathers – fluid substitution 6507/6-1
InSitu OIL GAS
Alternating sand/shale
Brighter response for HC, fairly flat AVO
6507/6-4S vs 6507/6-1 comparison6507/6-4S 6507/6-1
Sandier section in Sindbad, slightly more distinct shale packages
but thin and possibly below tuning
Slightly more marked AI contrast
AI AI
6507/6-4S modeling
Synthetic modeling of Sindbad logs
show slight brightening with offset
AI
PR
Color-coded hard
stringers coinciding
with carbonate flags
Estimate velocity model below
Evaporites
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Sesam
Sindbad
Dolomite/Anhydrite
Biogenic gas
Grey Beds
Red Beds
Åre Fm
NW SE
Nearby well did not penetrate Permian
marker
Very little reflectivity or established
markers within the Red beds below the
Evaporites
Nearest Permian velocity control
several hundred km’s to north
VSP Overlay on Depth seismic
Anisotropic
PreSDM
Red line indicates actual Top
Carbonate (4119m TVDSS)
Long section to drill from
Triassic evaporites to
Permian marker without
correlatable reflectors
Estimates of anisotropy
uncertain
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Top Permian depth
Interpreted top carbonate came in deeper than expected (+261m TVD).
Possible explanations:
Incorrect anisotropy estimation for BCU to Top Anhydrite
Three intervals tested leading to a decision to choose a relatively high delta. However the
Top carbonate came in close to the isotropic velocity depth model. Interval between Top
Anhydrite and Top carbonate more or less isotropic. Weak lower Triassic reflector in offset
well not correlatable to Sesam well (basis for delta value below Top Anhydrite). Isotropic
PreSDM shows close to same (slightly less) thickness between Top Anhydrite and Top
Carbonate as encountered in the well. Smaller thickness in the isotropic PreSDM means that
the tomographic velocity was too low (negative delta is not realistic). Stacking velocity has a
large uncertainty for reflectors at 4km depth.
Velocity difference between 6-1 well and 6-4A.
Presence of high velocity stringers in 6-4A that in isolation are below tomographic resolution
The velocity model is not honouring the dip of the events and reflects a compaction trend.
Lithology below TD of offset well was unknown in terms of velocity. It contained considerable
marl content and anhydrite stringers.
Conclusions
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Sindbad tested an amplitude anomaly in the Grey beds of the Triassic on the Sør
High of the Nordland Ridge. False positive AVO effect due to tuning and/or
calcite stringers. Higher N/G than at 6507/6-1, indicating possible channel
penetration.
Although dry, the Sesam well penetrates a full Upper Permian sequence
including the P/T boundary and underlying Lower Permian/Carboniferous rocks.
The lower part of the sequence can be correlated to clastic rocks penetrated in
shallow IKU drill cores recovered close to the Norwegian mainland.
Depth conversion in regions with little/no well control remain challenging!
Charge and seal remain the key risks of the Triassic and the Permian on the
Nordland Ridge in the Norwegian Sea.
Acknowledgements
The presenter thanks E.ON E&P Norge AS for permission to present this
work.
The presenter also thanks current and former colleagues for their
contributions to the work performed in PL350, in addition to former license
partners Statoil and PGNiG.
Also thanks to the Organising Committee of the FORCE seminar
«Underexplored plays» for the opportunity to share the results of the
Sindbad/Sesam well on the Sør High of the Nordland Ridge.
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