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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Location

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Sindbad/Sesam

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

Permian outcrop –

Wegener Halvø,

East Greenland

6

80 m

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

1 – brine2 – light oil3 – heavy oil4 - gas

AVO product for 4 scenarios

NW SE

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.

Well Tie

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Chronostratigraphic correlation

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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