1 - Classification: Internal 2010-06-11

Ocean Bottom Seismic in the Oseberg South area

John Dangerfield, Jim Daniels, Per Riste, Mari Skaug and Vibeke Haugen

2 - Classification: Internal 2010-06-11

ΩC

GC

BJ

K

GØ

δ Oseberg Sør

R

3 - Classification: Internal 2010-06-11

Oseberg Sør

Many areas of bad data…But we have great production wells

C J

4 - Classification: Internal 2010-06-11

Series of down stepping fault blocks

Thin reservoirs – often little or no seismic expression

Increasing erosion of Brent to east

Omega

G-Central Tune

BCUDraupn

e/

Heather

UTarbertMT2

MT1LT

UNessLNess

Coal

Channel Sandston

e

J-StructureC-structureG-East

BCUDraupn

e/

Heather

UTarbertMT2

UNess

Coal

Channel Sandston

e

Geological cross section through Oseberg Sør

West East

5 - Classification: Internal 2010-06-11 C-structure F-12, F12A and F-12 B.

F-12 B: Success!

30/9-6 Exploration well

1 km

F-12: Water wet

F-12 A: No sand

Production profile F-12 B

0,

500,

1000,

1500,

2000,

jul-04 jan-05 aug-05 feb-06 sep-06

Sm

3/d

Actual

Predicted

3 wells, payback time 80 days

6 - Classification: Internal 2010-06-11

1 km

Dolomitised Oligocene sands

Poor image

7 - Classification: Internal 2010-06-11

50 meters away

Poor image

50 m away

1 km

8 - Classification: Internal 2010-06-11

Sonic logs

1500 5000 m/s

30/9-6 30/9-13S

1500 5000 m/s

Thin dolomitised sands

Destroy the seismic image

9 - Classification: Internal 2010-06-11

Top Shetland beneath an Oligocene sand

Effect of dolomitised sands on the Seismic gathers

10 - Classification: Internal 2010-06-11Acquired N-S Acquired E-W

Dolomite sand Dolomite sand

The same seismic line…

Different imageDifferent image

30/9-6 30/9-6

11 - Classification: Internal 2010-06-11

Shots Receivers

Effects of shooting orientation

Reflection point

Reflection point

Dolomite sands

Dolomite sands

12 - Classification: Internal 2010-06-11

Seismic

5000 m/s sand

Sand model generated from surface seismic

2000 m/s overburden

Model

13 - Classification: Internal 2010-06-11

Top Shetland model (no sand)

14 - Classification: Internal 2010-06-11

Overburden sands

15 - Classification: Internal 2010-06-11

Magnified model

Apparent faults Pull-up Low amplitude

Top Shetland

16 - Classification: Internal 2010-06-11

Real gathers

Model gathers

The model looks like the real data

17 - Classification: Internal 2010-06-11

(11)

(3)

(5)

(7)

(1)Number of Azimuths

FOLD

25

75

125

175

225

Model stack of Top Shetland with different numbers of azimuths

Conclusion: Minimum 7 well spaced azimuths

required

18 - Classification: Internal 2010-06-11

What is OBC?Seismic receivers are on the seafloor

Records both P-wave (compression) and S-wave (shear)

We shoot crossline to get multiazimuth coverage

Receivers

Shot points

from PGS

19 - Classification: Internal 2010-06-11

Top Reservoir

C-structure

30/9-6

20 - Classification: Internal 2010-06-11

OBC gather

Single gather

2.5 kmTop Reservoir

C-structure

With dolomite

sands

Multi-azimuth gives much better

illumination

21 - Classification: Internal 2010-06-11

OLD DATA2005 OBC DATA

Dolomite sands

C-structure

Reservoir section

C-structure

30/9-6

22 - Classification: Internal 2010-06-11

Marine data, reservoir section

OBC data, reservoir section

Base Cretaceous

Top Lower Tarbert

23 - Classification: Internal 2010-06-11

2005 Model – Streamer 2007 Model – OBC

C – STRUCTURE (same interpreter)

24 - Classification: Internal 2010-06-11

C-structure OBC 2005 (25 Km2)

J-structure OBC 2008 (76 km2)

OBC surveys Oseberg Sør

OBC surveys potential base 4D OBC surveys

25 - Classification: Internal 2010-06-11

Streamer

NH9802

Six cable marine acquisition

Time migration

26 - Classification: Internal 2010-06-11

2008 OBC

ST0823

OBC acquisition

Fastrack PreSDM migration

Processed in 6 weeks

27 - Classification: Internal 2010-06-11

2008 OBC Streamer

28 - Classification: Internal 2010-06-11

2008 OBC Streamer

Oseberg Area Unit RC meeting 27.05.2009

29 - Classification: Internal 2010-06-11

OBC NS and EW surveys Streamer 2004

30 - Classification: Internal 2010-06-11

2006 Model – Streamer data 2009 Model – OBC data

J – STRUCTURE (same interpreter)

31 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

32 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

33 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

34 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

35 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

36 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

37 - Classification: Internal 2010-06-11

Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features

38 - Classification: Internal 2010-06-11

Why OBC?

• Multiazimuth illumination:

− Better structural image, better horizon identification, better investment decisions

• Inversion is better: low frequencies, complete far offsets, S-wave data.

− Possibility to identify sands and fluids

• Monitoring production and injection effects:

− Accurate 4D repeat position, plus PS data, no platform hole

• Can be cheaper!

− Sparser acquisition, less weather downtime, no 3D and 4D infill,

39 - Classification: Internal 2010-06-11

what we aspire to:• Accurate maps for reservoir modelling

• Accurate prognoses for planned wells (including drilling hazards)

• Accurate lithology and fluid prediction from seismic

• Production effects from 4D seismic

With a poor seismic image none of these goals is achievable

40 - Classification: Internal 2010-06-11

Seismic budget

Planning

Acquisition

Processing

Interpretation

Depth

Rock physics

Lithologies

Fluids

Production effects

41 - Classification: Internal 2010-06-11

Ocean Bottom Seismic in the Oseberg South areaJohn Dangerfield, Jim Daniels, Per Riste, Mari Skaug and Vibeke HaugenPresented by Dr Jim Daniels

Principal Geophysicist

jidan@statoil.com tel: +47 48151755

www.statoil.com

Thankyou

The authors wish to thank the following partners for permission to publish this data:

•ConocoPhillips Skandinavia AS

•Petoro AS

•Total E&P Norge

•ExxonMobil Exploration and Production Norge AS.

The conclusions drawn are those of the authors alone.

42 - Classification: Internal 2010-06-11Classification: Internal 2010-05-03