Illumination Based Seismic Imaging of fractured basement using Wave theory

Yasir Bashir (PhD in Petroleum Geoscience)

Supervisor: Prof. Dr. Deva GhoshCo-Supervisor: Dr. Chow Weng Sum

Research Title

Research Proposal Defence

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Outline

• Introduction• Problem Statement• Objectives• Literature Review

• Case study

• Methodology• Preliminary Results• Time Line• References• Comments and Suggestions

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Introduction

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• Geophysical Challenge in Malay and adjacent basin.

• In Basement Seismic Imaging is affected by • Lack of bedding• Highly dipping fault and fracture• Small impedance contrast• Basement heterogeneity• Fracture Distribution• Their connectivity• Lateral variation

• Difference between good and dry well?

• Regular Seismic methods

• Wave-Equation Migration. (One-way and two-way)

Literature Review Geology of Malay Basin

• Malay Basin, a northward-trending

pull-apart extensional rift basin.

• Formed during the late Eocene-early

Oligocene

• Underwent thermal subsidence and

sedimentation during the early Miocene.

• Groups starting from the youngest (A) to

the oldest (M).

• Exploration currently focuses primarily

on groups E–K.

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China: Daminton depression-produced oil from fractured metamorphic (500m oil column).

Thailand: Phitsanulok basin, produced oil from fractured Metamorphic

Vietnam: Cuu Long basin, oil from fractured granite.

Indonesia: Central Sumatra and South Sumatra basins, oil/gas from fractured Metamorphic/granite.

Algeria: Ghadamas basin, oil from fractured Cambrian sandstone.

Malaysia: Malay basin, oil from fractured metamorphic. Future remaining play in Carigali exploration acreages. Sudan, elut basin, heavy oil from fractured granite. Anding Utra: Fractured Jurassic Metamorphic

Basement

Literature Review Cont.…List of countries proven play in fracture reservoir

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Petroleum geology and resources of Malaysia

Problem Statement

Reflection event form the basement can not image properly in regular seismic data processing technique.

Reliable methods/algorithms are required to illuminate the fracture basement.

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Objectives

Better definition of faults/fracture zones inside Meta-sediment

Basement through

Careful pre image processing.

Develop Appropriate and reliable Depth Migration Algorithm

and apply for fracture basement imaging.

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Classification of Seismic Imaging

Full

High Frequency

Literature Review Cont.…

8 D.P. Ghosh

Kirchhoff PSTM

WEM

“full” Beam PSDM

Kirchhoff PSDM

Reverse TimeMigration (RTM)

Complexity increasing

“Fast” Beams

Complexity comparison (Migration Methods)

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Literature Review Cont.…

Angle of Dipping 800

Acoustic Wave Theory (derivation of wave equation)

Hooke’s Law : Volume change is proportional to pressure

(1)

Newton’s Law : Net Force is equals to mass times acceleration

(2)

Using ∆ m = ρ v

(3)

Combining (1) and (3) we have the Wave Equation as :

= 0 where, c²= k / ρ (4)

Taking Fourier Transform of (4) we get:

Which is known as the Helmholtz Equation

(5)

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Literature Review Cont.…

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Comparison Between One-Way and Two-Way Wave Equation using 2 layer Model

Application of One-way and Two-way wave equation

Velocity model with an interface at a dip angle of 60◦.

Migration images for a dipped interface at 40◦. At this dip, the one-way migration still produces an

acceptable result.

Case Study Cont....

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Angle of Dipping 400

Comparison between angle Of Dipping

Migration images for a dipped interface at 60◦. At this dip, the one-way migration still produces an acceptable result.

One-way migration breaks down and two-way migration still reproduces the dipped interface but suffers from illumination problems.

Case Study Cont....

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Angle of Dipping 600 Angle of Dipping 800

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Figure. Comparison of 2002 and 2006 Kirchhoff depth migration on a vertical sectionFigure. Comparison of 2002 and 2006 Kirchhoff depth migration on a vertical section

Figure. Comparison of 2002 and 2006 CBM depth migration on a vertical section Figure. Comparison of 2002 and 2006 CBM depth migration on a vertical section

Case Study Cont....

Results from cuu long basin (Vitname)

Both Migration MethodsImprovement in 2006

Limitation

KirchhoffCBM

Results

CBM is used to image the top of basement and fracture inside the basement by applying different velocity model.

(Pham, Sun et al. 2007)

Time Slice showing better imaging inside the basement fracture. Controlled Beam Migration (CBM) gives the good result to image the top of the

basement and the fractures inside the basement. The image quality of CBM is superior to that of Kirchhoff migration.

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Figure . Comparison of 2002 and 2006 CBM depth migration on time slicesFigure . Comparison of 2002 and 2006 CBM depth migration on time slices

Case Study Cont....

Conclusions

Scope of Research

The results obtained from research will be helpful in selecting the best methods for imaging the fracture basement.

The results will be help to image the fracture basement and adjacent formation including complex structure and boundaries which are poorly resolved using regular seismic processing techniques.

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Methodology

For getting preliminary results I use the velocity and density model to propagate the wave.

2 layer model one is horizontal layer and other is dipping layer at 60 degree.

Wave Propagation In 2 layer model

Preliminary Results

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Kirchhoff PSTM on a two layer model

Figure. Showing velocity model and geometry of source receiver

Figure. Showing processed gather before migration

Figure. After applying the KPSTM migration

Preliminary Results

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Conclusion

Kirchhoff PSTM couldn’t illuminate because of dipping angle, So wave equation gives the

satisfactory results in this case.

Double Radical Equation:

Preliminary Results

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Diffraction curves

Diffraction behavior, velocity= 2000 m/sec diffraction behavior, velocity= 3000 m/sec

Diffraction behavior, velocity= 4000 m/sec Diffraction behavior, velocity= 5000 m/sec

Preliminary Results

Diffraction Curves

Diffraction Behavior, velocity= 2000 m/sec diffraction Behavior, velocity= 3500 m/sec

Diffraction Behavior, velocity= 5000 m/sec

On X-axis we have offset in km and Y-axis time in second. So the result and observation from this diffraction curve are as under.

 ConclusionOnly velocity does not effect on diffraction but depth also.If velocity is constant and depth is increasing then diffraction curve spread out and curvature will decrease.Diffraction give a hyperbola on the edge of the reflector also on the whole reflector points but because of phase change they cancel out only edge hyperbola remain.

Preliminary Results

Seismic Response

Geology

Seismic Response to Geology (Diffraction Example)

Time Line

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Comments

&

Suggestions

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