Ocean bottom seismic in the oseberg south area j daniels

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


ΩC

GC

BJ

K

GØ

δ Oseberg Sør

R


Oseberg Sør

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

C J


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


1 km

Dolomitised Oligocene sands

Poor image


50 meters away

Poor image

50 m away

1 km


Sonic logs

1500 5000 m/s

30/9-6 30/9-13S

1500 5000 m/s

Thin dolomitised sands

Destroy the seismic image


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


Shots Receivers

Effects of shooting orientation

Reflection point

Reflection point

Dolomite sands

Dolomite sands


Seismic

5000 m/s sand

Sand model generated from surface seismic

2000 m/s overburden

Model


Top Shetland model (no sand)


Overburden sands


Magnified model

Apparent faults Pull-up Low amplitude

Top Shetland


Real gathers

Model gathers

The model looks like the real data


(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


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


Top Reservoir

C-structure

30/9-6


OBC gather

Single gather

2.5 kmTop Reservoir

C-structure

With dolomite

sands

Multi-azimuth gives much better

illumination


OLD DATA2005 OBC DATA

Dolomite sands

C-structure

Reservoir section

C-structure

30/9-6


Marine data, reservoir section

OBC data, reservoir section

Base Cretaceous

Top Lower Tarbert


2005 Model – Streamer 2007 Model – OBC

C – STRUCTURE (same interpreter)


C-structure OBC 2005 (25 Km2)

J-structure OBC 2008 (76 km2)

OBC surveys Oseberg Sør

OBC surveys potential base 4D OBC surveys


Streamer

NH9802

Six cable marine acquisition

Time migration


2008 OBC

ST0823

OBC acquisition

Fastrack PreSDM migration

Processed in 6 weeks


2008 OBC Streamer


2008 OBC Streamer

Oseberg Area Unit RC meeting 27.05.2009


OBC NS and EW surveys Streamer 2004


2006 Model – Streamer data 2009 Model – OBC data

J – STRUCTURE (same interpreter)


Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate

Inversion resultsSuggest fluvial features


Gas sand

Oil sand

Water sand?

Shaley sand

Shale

Carbonate



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,


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


Seismic budget

Planning

Acquisition

Processing

Interpretation

Depth

Rock physics

Lithologies

Fluids

Production effects


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

Principal Geophysicist

[email protected] 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

Ocean bottom seismic in the oseberg south area j daniels

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