PJ Boult Page 1PESA DL 2009

In requesting the services of GINKGO ENP GNG the client agrees that GINKGO ENP GNG is acting in an advisory capacity and shall not be liable or responsible for any loss, damages or expenses incurred by the client, or any other person or company, resulting from any data or interpretation presented in this report.

Introduction to seismic structure interpretation methods and assessment of trap integrity in exploration and baffles

to production.

forPESA

byDr Peter Boult

GINKGO ENPGNG

October / November 2009

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Acknowledgements

• Graham Yielding (Badleys Geoscience)

• Brett Freeman (Badleys Geoscience)• John Walsh (FAG Dublin)• Quentin Fisher (Leeds RDR)• SANTOS• Rodinia Oil Corp (Calgary)• Meridian Petroleum (UK)• Adelaide Energy

Permission to reproduce material in this PESA DL course has been granted by

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Seismic Structure

• Introduction

– Basic fault and fold terminology.

– Why do some rocks fold while others fracture?

• Using 3D folds axial surfaces of to get better 2D

maps

– Locating axial surfaces in seismic sections

– A novel (better?) interpretation workflow for folds in

2D data

• Lessons - mapping folds

• Introduction to faults– Why and how do they form– What do they look like

• Normal faults• Reverse fault• Strike-slip faults

– Relays– Duplexes

• Exercise

• Seismic structural interpretation in complex

faulted settings

– Interpretation workflow recommendations

• Geometric considerations

• Seismic processing considerations

– Checking your interpretation for geological plausibility

• Kinematic considerations

• Exercise

• Fault seal classification• Lithification:

– Rock deformation – brittle or ductile? • Fault seals in exploration

– Primary analysis – juxtaposition– Secondary analysis

• Fault rock analysis• Fault reactivation / top seal failure

– Case study• Fault seals in production

– Methods for incorporating faults into production simulation models

– Case study • Exercise

• Calibration

• Asking the right questions

• Evidence-based approach to fault seal

analysis

• Validation

– Exploration

– Production

• Concluding remarks

Workshop 1 Workshop 2

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Seismic Structure in Petroleum Exploration &

Production?

• Structural traps make up 95% of reservoirs

• Fold and fault mapping is a crucial, though very underrated step in the structural geological workflow in exploration and production.

• Provides the foundations for all subsequent analysis and modelling

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Why is Fault and Fault Seal Analysis important?

• Faulting issues impact on >70% of reservoirs

• Petroleum Exploration– Faults often form one of the main seals for reservoirs

– Faults are often invoked as conduits for petroleum migration

– Faults may allow the leakage of petroleum through top seals

• Petroleum Production

– Faults can severely retard fluid flow resulting in compartmentalisation

– Many companies have had to lower their reserve estimates due to fault-related compartmentalisation

– Effective production strategies require understanding of fault behaviour

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Why do some rocks fault while others fold?

• Substance– Minerals– Porosity

• Temperature• Confining pressure• Strain rate

Transition from elastic to ductile OR brittle depends on:-

Str

ess

Ela

stic

Ductile

Brittle

Elast

ic

Strain

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In requesting the services of GINKGO ENP GNG the client agrees that GINKGO ENP GNG is acting in an advisory capacity and shall not be liable or responsible for any loss, damages or expenses incurred by the client, or any other person or company, resulting from any data or interpretation presented in this report.

Seismic Structure - folds

• Using 3D folds axial surfaces of to get better 2D maps

– Locating axial surfaces in seismic sections

– A novel (better?) interpretation workflow for folds in 2D data

• Lessons - mapping folds

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Folds in seismic sectionsFolds can be classified based on whether or not the thickness of stratigraphic layers changes over various dip domains OR across axial surfaces

T2 = T1 γ1 = γ2T2 > T1 γ1 < γ2

Diagrams from Shaws et al, 2005

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Fold models and processes

Flexural or bedding plane slip

Ductile

T2 = T1 γ1 = γ2

T2 > T1 γ1 < γ2

Diagrams from Shaws et al, 2005

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Locating axial

surfaces in seismic sections

Migration moves dipping reflectors upward and laterally to properly image the fold geometry.

Reflections on non-migrated OR UNDERMIGRATED sections do not accurately represent fold shape.

However, the axial surfaces can still be interpreted by mapping the truncations of the HORIZONTAL reflections

Diagrams from Shaws et al, 2005

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Compression of domino basement blocks – with some strike-slip movement

Axial planes propagate from discontinuities of rigid basement.

Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

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But how should we create a map out of data like this? Aliasing problem!

Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

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1200 x 12002400 x 2400

Lots of bulls eyes

4800 x 4800

At half the line spacing the gridding bulls eyes have almost gone.

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4800 x 4800

But individual structures bear little resemblance to folds

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So what’s the best way to deal with this situation?

Put the fold axes on

Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

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Line fold axial traces up in 3DCorrelate fold axes Add horizon axial traces

Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

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Using horizon axial traces as well as 2D horizons give more control when gridding

Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

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Not a fold just a bend in the seismic

Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd.

Top reservoir horizon

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Map using horizon axial trace control

600 x 300

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600 x 300 45 degs rotation with fold axes – BUT NO Z DATA

Just for comparison – using the horizon based fold axial traces – BUT NO Z DATA

1200 x 600 45 degs rotation with fold axes – BUT NO Z DATA2400 x 1200 45 degs rotation with fold axes – BUT NO Z DATA

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Lessons - mapping folds• Correlation should be done in True Perspective

3D– Consider en-echelon nature of folds IN OUTCROP– Line up fold axes and extract horizon-based axial

traces

• Need to grid at the correct scale– Normally ½ 2D line spacing– BUT when fold axis are used, can go down to much

smaller grid without bulls eyes.

• BEST to use a grid cell with its longer dimension along structural grain

• However, EVEN BETTER to combine above with use of Z data on horizon-based axial traces

• Z data best created in 3D interpretation package