flyndre field – tilted oil water contact in a thin palaeocene sandstone...

Flyndre Field – Tilted oil water contact in a thin Palaeocene sandstone reservoir

Finn Engstrøm1, Thomas Dons Demsig2, Gerhard Templeton2 and Henk Wilms2

1Maersk Oil, Copenhagen, 2Maersk Oil, Aberdeen

Acknowledgement: Maersk Oil, Talisman Energy (UK) Limited, Eni UK, Noble Energy, Skeie Energy, Noreco, StatoilHydro and Petoro

Agenda

Introduction / Flyndre - Location and Geology

Drilling History / Pressure and Saturation Observations

Summary of Pressure and Saturation Observations

Potential Explanations for Observations

Causes for hydrodynamics

Conclusions

Flyndre Field Location

Flyndre Regional Setting 16 km

SSW NNE

Mid Miocene U/C

T. Oligocene

T. Eocene

T. Lwr. Eocene

Chalk L. Cret

U. Jur Zechstein Salt

Triassic

Rotliegend

ORION

Top Balmoral Sand Top Tor Chalk Palaeocene

30/18-2 Projected

30/18-3

FLYNDRE

30/14-2 30/14-1 N1/5-2

Low relief 4-way dip closures formed by compactional drape above deep

Mesozoic salt domes.

TD 15266

TD 14942

TD 9844

TD 12557

TD 13969

Paleogene Central North Sea Lithostratigraphic Scheme

•  Lista Formation

−  Deep water hemi-pelagics.

•  Upper Balmoral Sandstone Unit

−  Composite sharp based upward

fining sandstone unit 20ft to 30ft

thick

−  Turbidites

−  Total porosity ~22 pu

−  Liquid permeability ~ 10 mD

•  Lower Balmoral Sandstone Unit

−  Dominantly debrites in this distal

area.

−  Poor reservoir quality.

Permeability of Balmoral Sandstones

Kah vs Porosity & Shaliness

0.001

0.01

0.1

1

10

100

1000

10000

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Porosity ( )

Kah

(mD)

Clean1-5% Vshale5-10% Vshale10-15% Vshale15-20% Vshale20-25% Vshale25-30% Vshale30-35% Vshale35-40% Vshale40-50% Vshale50-60% Vshale60%+ VshaleVshale = 0%Vshale = 30%

Shale Line

Clean Sst Line

Flyndre / Oil Permeability / De-Saturation 2

0.01

0.1

1

10

100

1000

0.1 1 10 100 1000

Ka (mD)

Ko

(mD

)

Expectation

Equality Line

Ko = 0 assymptote

Ko(swi) after first mineral oilflood - 30/14-2Ko(swi) after 2nd Mineral OilFlush - 30/14-2Ko(Swi)- OWR 30/14a-1

Ko(Swir) - OWR 30/14a-1

Ko(Swi) Wettability 30/14a-1

Ko(swir) - extr. afterdesaturation - 30/14-2Ko(swi) before gas RP

Ko(Swir)extr. before GO RP

Non- Reservoir

Agenda




Potential Explanations for Observations

Conclusions


Well Location Map and Drilling History

Flyndre

30/14-3, 2007 ODT @ 9725’ Oil pressure

30/14-3z, 2007 ODT, Hrz well Oil pressure

N 1/5a-2, 1974 Non reservoir No Contact, no Pressure

30/13-7, 1997 Water bearing WUT @ 9740’ Water pressure

UK No

30/14-1, 1989 ODT @ 9617’ Oil Pressure

30/14-2, 2004 OWC @ 9594’ Oil pressure

Josephine

30/13-1, 1970 WUT @ 9484’

Depth structure map Near Top Balmoral Sand

2km

0 20000 40000 600009000 9500 10000 105000 0.2 0.4 0.6 0.8 1

9500

9600

97000 0.1 0.2 0.3 0.4 0.5

9500

9600

97000 0.2 0.4 0.6 0.8 1

AI (us*gm/ft*cc)

Well: 30/14-2 (Flyndre) Ft TVDss-Plot

Vshale ( ) Porosity ( ) Saturation ( ) Depths (ft tvdss)

Lista

Balmoral sst

OWCa

Base Balmoral

DT GR RES NEU DEN

30/14-2 Balmoral Sand & OWC

9682’ – 9700’

9758’ – 9698’

Present Day OWC

Base Balmoral Sand

PHO

TO

Base Debrite

Palaeo ODT, Oil Stain Occurs To The Base Of the Turbidite

Top Upper Balmoral Sst.

Top Lower Balmoral Sst.

OWC

25.4% 79.9mD

24.6% 44.4mD

24.9% 64.1mD

23.1% 38.2mD

26.7% 218mD

28.4% 266mD

27.1% 604mD

25.8% 328mD

25.5% 375mD

20.2% 24.5mD

23.8% 192mD

27.3% 302mD

25.5% 74.3mD

26.1% 154mD

27.8% 106mD

22.5% 106mD

24.7% NA

23.7% NA

23.8% 3.7mD

Balmoral sst

Base Balmoral sst

9400

9500

9600

9700

9800

99000 20000 40000 60000

9400

9500

9600

9700

9800

99000.00 0.25 0.50 0.75 1.00

9400

9500

9600

9700

9800

99000.00 0.10 0.20 0.30 0.40

9400

9500

9600

9700

9800

99000.00 0.25 0.50 0.75 1.00

AI (us*gm/ft*cc)

Balmoral Sst / Flyndre

Vshale ( ) Porosity ( ) Saturation ( )

30/14-1 N1/5a-2 30/13-7 30/14-2 30/14-3

N S Flyndre

9450

9500

9550

9600

9650

9700

9750

9800

9850

Dep

th ft

. TV

Dss

30/14-2

N1/5a-2

30/14-1

30/14-3Z

30/14-3

WUT 9740’

ODT 9566’

ODT 9725’

ODT 9617’

Non-net

OWC 9594’

30/13-7 Flyndre spill - 9730’ TVDss

Flyndre Hydrocarbon Contacts

Simplified MDT-data overview

•  Limited Oil column

•  No Water Points. Waterline based on the regional aquifer pressure map.

•  Some data points are uncertain

•  Pressure defined and sat-height model defined FWL’s in agreement (+/- 15 ft)

MDT-Pressures / 30/14-19500

9550

9600

9650

9700

9750

98006750 6770 6790 6810 6830 6850 6870 6890

Depth (ft tvd ss)

Pres

sure

s (p

sia)

U ni t s

F o rmat io ns

A l l P r es s ur es

O i l -‐ L i ne

W at er -‐ L ine

P r es s ur e F W L

Agenda




Potential Explanations for Pressure Observations

Conclusions


6844

6830

6850

Orion 6470-6613

Joyce 6809

6869

6853

6840

Recorded/Inferred Balmoral Aquifer Pressures @ 9700 ft tvd ss

Aquifer pressures decrease from NE -> SW

Water pressure Inferred Water pressure

2km

Agenda



Summary of Pressure Observations


Conclusions


Compartmentalization?

For •  May explain different OWCs Against •  Cannot explain variations in

aquifer pressures •  No seismic evidence of large scale

faulting •  Can only with difficulty explain

the presence of remaining oil at the base of 30/14-2

Indifferent •  No significant differences in PVT

or isotopes •  No compartmentalization

identified along 30/14-3z

Through going fault creating two oil pools

30/14-2 OWC (9594 ftss)

Spill depth (9730 ftss)

2km

Perched Water?

For • May explain variations in

active OWC’s Against •  Cannot explain the

presence of remaining oil below active OWC in 30/14-2

•  Cannot explain observed variations in aquifer pressures

Oil

Free Water

Perched Water

Hydrodynamics ?

For •  A SW-trending hydrodynamic

gradient can explain observed variations in active OWC

•  A change (increase) in hydrodynamic gradient can explain the presence of remanining oil in 30/14-2

•  Regional mapping of Balmoral aquifer pressures agree with the presence of active hydrodynamics

6844

6830

6850 Orion 6470-6613

Joyce 6809

6869

6853

6840

Datum Depth = 9700 ft tvd ss

2km

Agenda



Summary of Pressure Observations


Conclusions


Balmoral Sand Regional Pressures

O/P < 50 psi

Andrew/Balmoral Sandstone limit

O/P < 50 psi

Greater Flyndre Field Area

O/P > 2000 psi Close to shale

pressures

• Highest overpressures in the Andrew/Balmoral sand units towards SE.

• Assumed driver for the flow of water in the Balmoral/Andrew sand units is expulsion of water from the shales (Swarbrick 2007)

• Inferred Balmoral aquifer pressures in the Greater Flyndre area agree with published map by Swarbrick.

From GeoPressure 2007 Report

Effect of Local Oil Pools in Balmoral

6830

6850

Flyndre Oil pool

10 psi/km

10 psi/km

5 psi/km

• 5-10 psi/km hydrodynamic gradients around Flyndre

• Oil pools may locally block for the flow of water in the aquifer and increase aquifer gradient

Change in aquifer gradient around Flyndre could suggest that the oil pools Limits the flow area

2km

Hydrodynamics in the Chalk

• Overpressure in the Chalk is often close to overpressure in the Paleocene sandstones

• Similar size and direction of the hydrodynamic gradient in Balmoral sst and the Chalk below.

From the Millennium atlas Are the observed hydrodynamics

in the Balmoral sst and the Chalk linked ?

General Model Hydrodynamics North Sea Basin

From Dennis 2003

Simple Model for Hydrodynamic Flow

Ekofisk, Tor and Hod Chalk

Balmoral sst

Overpressured Shales

Shales and Marls

Max Overpressure

1000-2000 bw/y

25-500 bw/y

30-150 bw/km/y

** Flow rates are for a 1 km wide model

30-150 bw/km/y

However, • Flow of water from the shales above a Balmoral oil pool

or from the chalk below will add to the complexity of the hydrodynamics conditions

Top Chalk Balmoral sst

FWL Due to regional hydrodynamics

Local change of FWL due to relative permeability effects

Hydrodynamic Concept Tested by Reservoir Simulation

hydrodynamic gradient

5700 m 9786 ft tvd ss

9596 ft tvd ss

Conclusions

• Observed variations in fluid contacts/pressures in Flyndre are more likely due to hydrodynamic effects than compartmentalization and/or perched water.

• A horizontal OWC in a thin permeable sandstone reservoir, embedded in shales, is rather an exception than the most likely.

Thank you for your attention -  Any questions?

Disclaimer: The views in this presentation are those of the authors and do not necessesarily represent those of Maersk Oil or the Flyndre partners

flyndre field – tilted oil water contact in a thin palaeocene sandstone...

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