gl_seismic_dp_20140313

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SEISMIC DATA PROCESSINGfor Oil & Gas Exploration

Universitas BrawijayaMalang, 15 March 2014

Teguh SurosoHAGI – Pertamina UTC

HAGI Guest Lecturing Program

Outline

Introduction

Fundamentals

Concepts

Seismic data processing in practice

Advanced processing

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INTRODUCTION

Advanced ProcessingBasic Processing

Field records

Time migrated section

Depth migrated sectionVelocity model building

Acoustic Impedance section

AVO analysis

Well seismic tie

Intercept-Gradient sectionTime migrated gather

Acquisition

Seismic Products

Final CMP Gathers

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Diephuis, 2008 : To transform the raw field records into an interpretable volume/line depicting

reflection coefficient in the subsurface

Gluyas & Swarbrick, 2004 :To enhance the interpretable (useful) seismic information relative to the noise in

the signal and place the reflectors in their correct x,y,z space

IPIMS, 2010 :The main goal of seismic processing is to obtain the best image of the

subsurface.

Reservoir characterization:- AVO and Inversion

Seismic DP Purposes

Shot Point

Ch-1 Ch-n

Sample of Field Record

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Geology Model

Field Record – along the lineDisplayed in every 10 SP

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NOT interpretable data

Overlay field records with geology model

Seismic imaging, final product of processing

Overlay field records with geology model

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Interpretable data

Field record

Seismic imaging (stacked trace)

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Field record

Seismic imaging (stacked trace)

FUNDAMENTALS

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Seismic Wave

Seismic wave is a sound wave

Wave propagation is three dimensional phenomenon

Seismic wave

Body wave

Surface wave

P‐wave

S‐wave

Love wave

Rayleigh wave

Type of seismic wave

Seismic Wave IlustrationBody waves

Propagate through the Earth’s interior

a. P‐wave

> Compressional wave = longitudinal wave

> Propagates in solids, liquids and gasses

b. S‐wave

> Shear wave = transversal

> Propagates in solids only

Surface waves

Propagates along the Earth’s surface

c. Love wave

> low velocity layer overlaying high velocity layer

d. Rayleigh wave

> ground roll

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Body Wave Velocity Comparison

Propagation of P‐wave Propagation of S‐wave

S‐waves propagate more slowly than P‐wavesVs < Vp

Wavefront-Surface of equal time

source surface

Ray path-Line everywhere perpendicular to wavefront

Isotropic media

Wave Propagation

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P‐waveIf P-wave strikes a boundary

between two media with different velocities of propagation and/or different densities,

the P-wave will be :reflected, transmitted, and converted into reflectedand transmitted S-wave

The sum of the reflected andtransmitted amplitudes is equalto the incident amplitude.

Reflection & RefractionIf amplitude of incident wave = A0

amplitude of reflected wave = A1, andamplitude of transmitted wave = A2

A0 = A1 + A2

Relative size of the reflected and the transmitted amplitudes depend on The contrast in acoustic impedance

Acoustic Impedance (AI)

AI = ρ . V

ρ = density V = P-wave velocity

Reflection Coefficient (RC)

R = A1/A0

Transmision Coefficient (TC)

T = A2/A0 T = 1 - R

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Snell’s Law the reflected angle is equal to the incident angle

Head wave

critical angle

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Huygens’ Principle

Every point on an advancing wavefront is a new source of spherical wave.

Huygens’ Principle provides a mechanism

by which a propagating seismic pulse

loses energy with depth.

Seismic waves propagate away from the source :

- the wavefront become larger

- the surface become larger

- energy per unit area become smaller

Spherical (geometrical) spreading

Seismic amplitudes are proportional to the square root of energy per unit area.

Fermat’s PrincipleA light ray traveling from one point to another will follow a path

such that, compared with nearby paths, the time required is either a minimum or a maximum or will remain unchanged (Danbom, 2007)

Minimum time path (Diephuis, 2008)

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CONCEPTS

83m

Considera single sine wave of 30HzIn a medium of 2500m/s

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Menurut Rayleigh, agar dapat resolved: ketebalan lapisan harus setidak-tidaknya ¼ (Sherriff, 1997)

Resolusi

Resolusi Data SeismikHarris dan Langan (1991)

Dalam kaitannya dengan resolusi vertikal:

Data seismik antar‐sumur mengisi gapantara VSP dan log sonik

Resolusi maksimum : ~1 m

Fraksi reservoir: 10‐2 –10‐5

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Harris dan Langan (1991): Perbandingan resolusi seismik‐permukaan, seismik antar‐sumur dan log sonik

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*

AI(t) RC(t) W(t) S(t)

M O D E L I N G

I N V E R S I O NGeologic model

Convolutional Model

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Geologic model

Convolutional Model

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*


Geologic model

Convolutional Model

RC(t) S(t)AI(t)

Geologic model

Convolutional Model

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RC(t) S(t)AI(t)

Geologic model

Convolutional Model

RC(t) S(t)AI(t)

Geologic model

Convolutional Model

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AI(t) RC(t) S(t)

Geologic model

Convolutional Model

AI(t) RC(t) S(t)

Geologic model

Convolutional Model

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*


FORWARD MODELING

I N V E R S I O N

Seismic trace S(t) = RC(t) * W(t) + n(t)

n(t) = noise

Geologic model

Convolutional Model

Signal

Time domain

- Amplitude vs Time

Frequency domain

- Amplitude vs Frequency

- Phase vs Frequency

Signal Domain

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sum

Single frequency sinusoids sum

- A TIME domain wavelet can be synthesized by summing a set of single FREQUENCY sinusoids

- A TIME domain wavelet can be decomposed into a set of single FREQUENCY sinusoids

decompose

Fourier Transform

Inverse Fourier

Transform

Relationship Time‐Frequency

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Semakin banyak frequency contain-nya, gelombang seismik akan semakin spike,Sehingga daya-pisahnya semakin besar.

Simple quiz: Gambarkan bagaimana kira-kira sketsa spektrum amplitude-nya!

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Relationship between Time and Frequency domain

sum




Inverse Fourier

Transform





decompose

Fourier Transform

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sum




decompose

Fourier Transform

Inverse Fourier

Transform

Seismic signal

Change in amplitude with TIME

at a particular LOCATION

Change in amplitude with DISTANCE

at a particular TIME

T-domain (time)

X-domain (space)

Time domain

- Period (T) = time required to complete one cycle

- Frequency (F) = number of cycle/second

Space domain

- Wavelength ( λ ) = distance required to complete one cycle

- Wavenumber (k) = number of cycle/unit distance

Time Domain

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Xmin XmaxOffset

T i m

e

Time Domain

T-X domain F-K domain

aliased

Signal is crossed by noise in T-X plane but separated in F-K plane

Transformation T‐X to F‐K

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Sourcestrength absorption

scattering

Curved reflector

Amplitude variationwith angle (AVA)

Dynamic range Receiver responseReceiver strength

Geophone arrays

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SEISMIC DATA PROCESSING IN PRACTICE

PREProcessing

Pre-Migration

Migration

Post-Migration

Archieving

Data Preparation

Processing Stages

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PREProcessing

Pre-Migration

Migration

Post-Migration

Archieving

Data Preparation

Processing StagesNo. Items Remark

1 Survey type 3-D Land

2 Seismic data available Raw record from field tape

3 Data format SEG-D

4 Observer report available Softcopy & hardcopy

5 Geometry/navigation data available SPS

6 Field data available Elevation, Uphole time

7 Signature available for marine survey softcopy

8 Acquisition report available hardcopy

9 Field/On Board processing report available softcopy

10 Data legacy (from old process) available Post stack time migration volume (SEG-Y) from Elnusa.Powerpoint slides with interpretated lines

11 Other supporting data available -Well -Horizon interpretation

Standard Seismic Data Processing (Pre-Migration)ReformatingReformating

Geometry AssignmentGeometry Assignment

Trace Editing/DenoiseTrace Editing/Denoise

Geometric Spreading (Amp)Corr.Geometric Spreading (Amp)Corr.

Statics CorrectionStatics Correction

DeconvolutionDeconvolution

Velocity Analysis-1Velocity Analysis-1

Residual Statics Correction-1Residual Statics Correction-1

Velocity Analysis-2Velocity Analysis-2

Residual Statics Correction-2Residual Statics Correction-2

PREProcessing

Surface Consistent Amplitude Corr.Surface Consistent Amplitude Corr.

CMP GathersCMP Gathers

ReformatingReformating

Seismic-Navigation MergeSeismic-Navigation Merge

Trace Editing/DenoiseTrace Editing/Denoise

DesignatureDesignature

Swell Noise Attenuation, Linear Noise Attenuation

Swell Noise Attenuation, Linear Noise Attenuation

Tau-p DeconvolutionTau-p Deconvolution

Tidal CorrectionTidal Correction

SRME (if necessary)SRME (if necessary)

Velocity AnalysisVelocity Analysis

Demultiple (Hi-res Radon)Demultiple (Hi-res Radon)

Surface Consistent Amplitude Corr.Surface Consistent Amplitude Corr.


Geometric Spreading (Amp)Corr.Geometric Spreading (Amp)Corr.

DenoiseDenoise

Pre-Migration

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Standard Seismic Data Processing for Land2

Migration PreconditionMigration Precondition

Pre-Stack Time MigrationPre-Stack Time Migration


Post Stack Time MigrationPost Stack Time Migration

NMO, muting &Stacking


Pre-Stack Depth MigrationPre-Stack Depth Migration


Post Stack Depth MigrationPost Stack Depth Migration

NMO & muting &Stacking



Post Stack Processing :Noise Attn, Filter, Scaling Post Stack Processing :

Noise Attn, Filter, Scaling

Datum CorrectionDatum Correction

Final Volume/LineFinal Volume/Line





Depth to Time Conversion





Post Stack Processing :Noise Attn, Filter, ScalingPost Stack Processing :

Noise Attn, Filter, ScalingPost Stack Processing :

Noise Attn, Filter, Scaling Post Stack Processing :




Time to Depth Conversion





Final Volume/LineFinal Volume/Line Final Volume/LineFinal Volume/Line Final Volume/LineFinal Volume/Line

Offset RegularizationOffset Regularization





Standard Seismic Data Processing for Marine




Post Stack Time MigrationPost Stack Time Migration



Pre-Stack Depth MigrationPre-Stack Depth Migration


Post Stack Depth MigrationPost Stack Depth Migration




Post Stack Processing :Noise Attn, Filter, Scaling Post Stack Processing :


Final Volume/LineFinal Volume/Line

Velocity AnalysisVelocity Analysis Velocity AnalysisVelocity Analysis





Post Stack Processing :Noise Attn, Filter, ScalingPost Stack Processing :

Noise Attn, Filter, ScalingPost Stack Processing :










Final Volume/LineFinal Volume/Line Final Volume/LineFinal Volume/Line Final Volume/LineFinal Volume/Line

Offset RegularizationOffset Regularization

Residual (Radon) Demultiple








Gun & Cable CorrectionGun & Cable Correction Gun & Cable CorrectionGun & Cable Correction Gun & Cable CorrectionGun & Cable Correction Gun & Cable CorrectionGun & Cable Correction

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PREPROCESSINGSeismic Data Processing In Practice

Reformat

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Reformat: review loaded data

Continuous Analog Signal

Digitized Signal

Reconstructed Signal

Data Sampling

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Input

Output :

1ms sampling

Output :

2ms sampling

Output :

4ms sampling

Output :

8ms sampling

aliased

Memastikan sebelum resampling data di-Hi-Cut filter sekitar Frekuensi Nyquist

Frequency Aliasing

Geometry assignment-Geometry update.-Trace labelling.-Assign unique numbers.-Specify coordinate for all source & receiver position.

Data must be updated with the correct geometry. The wrong geometry assigned will be very fatal. The processing can not be continued to the next

step if the geometry is not correctly updated.

Geometry assignment

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Stack section with GEOMETRY ERROR

Incorrect geometry

Survey coverage

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SPS – Geometry file (XPS)

SPS – Header file Geometry/Navigation file

SPS – Receiver file (RPS)

SPS – Source file (SPS) Geometry/Navigation file

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Shot Point Gather with LMO applied showing GEOMETRY ERROR

Geometry QC

Shot Point Gather with LMO applied showing CORRECTED GEOMETRY

Geometry QC

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Distribusi fold kurang merata

Incorrect binning

Distribusi fold lebih merata

Correct binning

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Trace editing is the process of removing or correcting any traces or records which, in their originally recorded form, may cause a deterioration of the stack. Individual traces

may be affected by polarity reversals or by noise, (IPIMS, 2010).

Polarity reversal Noisy trace Spike

Trace editing

Raw record

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Denoising: low cut filter applied

Before Noise Attenuation in Shot Domain

Denoising

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After Noise Attenuation in Shot Domain

Denoising

Difference Noise Attenuation

Denoising

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Input

Processing:TransformationDenoiseFiltering

subtraction

Noise modeling

subtraction

Output

Denoising: noise modeling

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Denoising: low frequency target

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Before Noise Attenuation

Denoising: QC on stack

After Noise Attenuation


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Difference Noise Attenuation

beforeafterDifferences


“Smile” effect

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“Smile” effect removed

STATICS

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Shot record Before Statics Correction

Shot record After Statics Correction

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Koreksi statik, statik:

koreksi yang diterapkan pada data seismik untuk mengkompensasi efek dari variasi elevasi, low velocity layer (LVL) near surface, ketebalanlapisan lapuk dengan referensi sebuah datum.

Reflektor

SurfaceA

D

B

C

Travel time A ke B > Travel time C ke D

Responseismik

T0

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Surface

Reflektor

Respon seismik

Reflektor

SurfaceA

D

B

C

Travel time A ke B > Travel time C ke D.Perlu referensi yang sama

Datum

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Reflektor

SurfaceA

D

B

C

Travel time A ke B > Travel time C ke D.Perlu referensi yang sama

Datum

Bagaimana mengkompensasi bagian ini?

A’ B’ C’ D’

• Elevation Correction

• Delay-Time

• GLI (bagus untuk model layer-based)

• Traveltime Tomography (model grid-based bagus untuk complex geology)

• Waveform Tomography (lebih detail)

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HOW ABOUT MARINE DATA?

Water Column Statics Water column statics are a manifestation of physical changes in the water column caused by salinity, temperature, etc., over the period of acquisition. (Geotrace, 2010)

Statics on marine data

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To remove the dynamic temporal changes in seismic data due to velocity change in the water.

* WesternGeco, 2008

Before water velocity correction

After water velocity correction

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GunStreamer

Statics = (Streamer depth + Gun depth)/water velocity

Statics on marine data

STATICS QC ON STACK

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Stack without statics correction

Stack with statics correction

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Stack with residual statics correction

DECONVOLUTION

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Deconvolution :

- Improve the temporal (vertical) resolution

- Remove coherent noise of multiple

- Inversion process based on convolutional model of the seismic trace

S(t) = W(t) * R(t)

R(t) = S(t) * W(t)-1

Deconvolution :

1. Spiking Decon : the desire wavelet is a spike or impulse.

2. Predictive/Gap Decon : use early part of the trace to predict and deconvolve the later part.

3. Wiener Filter : designing a filter which when convolved with an input signal minimises the difference between actual output and the desired output.

4. Signature Decon : the output is desired wavelet.

Seismic source from dynamite Seismic source from vibroseis Seismic source from airgun

Deconvolution Parameters :

1. Length of input data window (gate).

2. Length of decon operator.

3. Whitenoise stability factor.

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Shot Point Gather without deconvolution

Shot Point Gather with deconvolution

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VELOCITY ANALYSIS

Why we need velocity?-Amplitude compensation-NMO correction (for stack)-Defining angle mute-Migration-Conversion to Depth-Identifying rock type

How to get the “correct” velocity?

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velocity too slow velocity too fastvelocity correctuncorrected

2264 m/s 2000 m/s 2500 m/sRaw

Overcorrected Undercorrected

(need to be slowed down) (need to be speeded up)

Velocity analysis

Tools in velocity analysis :-Semblance-CMP gather-Multi velocity function stacks-Control stack-Isovelocity overlay dengan control stack-Basemap

Survey 3-D

Survey 2-D

Velocity analysis

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Normally velocity increase with depth, this is becaused of overburden pressure effect

VelocityTime

Velocity analysis

Velocity analysis

containing multiple

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Velocity analysis

containing multiple

Velocity analysis

Multiples were removed

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Velocity analysis

QC: overlay velocity with the stack

Stack with single velocity function

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Stack with multi (analized) velocity function

AMPLITUDE CORRECTION

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- Also known as geometric spreading amplitude correction and true amplitude recovery (TAR).

- The Decrease in wave strength (energy per unit area of wavefront) with distance as a result of

geometrical spreading.

Amplitude (A) at time T ~ 1/r ~ 1/(V.T),

(r, is the radius of spherical wave front)

For a constant velocity medium, V=const.,

A(T) ~ 1/T

But when the velocity increases between layers, and in practice it increases with depth within layers,

A(T) ~ 1/TV2

Raw Shot Gather Less Compensation Good Compensation Too much Compensation

QC amplitude correction

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SURFACE PROBLEM

Stack without Surface Consistent Amplitude Correction (SCAC)

AFTER SURFACE CONSISTENT AMPLITUDE CORRECTION

Stack with Surface Consistent Amplitude Correction (SCAC)

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Shot gather without SCAC

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Shot gather with SCAC

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REGULARIZATION

Fold of coverage before 3-D Offset regularization

Fold of coverage before 3-D Offset regularization

Fold of coverage After 3-D Offset regularization

Fold of coverage After 3-D Offset regularization

Common Offset

Common OffsetRMS amplitude

After 3-D regularization

With offset regularization the data distribution in every single bin became “balanced”. And the QC on the RMS amplitude over the offset cube is very

usefull to look at the amplitude distribution before proceed the migration.

Offset regularization

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MIGRATION

Point reflector :the point at which the wavefront is reflected off the interface.Each source-receiver pair has a uniqe point reflector that yield the shortest traveltime .

Reaching the reflector, the wavefront will be reflected, andsome energy will propagate back to the source. The reflected wavefront will have the same circular form as the incident.

Migration Concept

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Migration Concept

Migration Concept

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Migration Concept

Migration Concept

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Migration Concept

Migration Concept

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Migration is a tool to get an accurate image of underground layer and structures.

Migration :-Geometric reposition of recorded events to their true position-Move dip events to their true position-Collapse the diffraction

Type of Migration :1. Kirchhoff

- Most popular in recent years- Trace by trace- Not the best for imaging complex structures or area with

strong lateral velocities variation

2. Finite-Difference (FD)- Much more accurate than Kirchhoff- Time consumming

3. Frequency-wave number or Fourier transform - More efficient than FD migration- More accurate than Kirchhoff- Not accurate for strong lateral velocity variation

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Migration

Post Stack

Pre-Stack

Input Data

Migration

2-D

3-D

Survey

Migration

Time

Depth

Domain

Migration Strategies (from Yilmaz, 2001)

Case Migration Strategies

Dipping events Time migration

Conflicting dips with different stacking velocities, complex non-hyperbolic moveout

Pre-stack migration

3-D behavior of fault planes and/or salt flanks 3-D migration

Strong lateral velocity variations associated with complex overburden structures

Depth migration

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MIGRATIONA

MIGRATIONB

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Post Stack Kirchhoff Time Migration result.

Pre-Stack Kirchhoff Time Migration gives benefit on the steep dip

structure. The good data will help the interpreter to produce more accurate interpretation. The accurate

interpretation of course will reduce the risk.

Migration Comparison

ANISOTROPYSpecial Processing

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www.treehugger.com

B

A

Thomsen (2002) :

Anisotropy is the variation of a physical property depending on the direction in which it is measured.

Seismic anisotropy is defined to be the dependence of seismic velocity upon angle.

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Isotropic

P-wave propagation

Anisotropic

X

Z

X

Z

Axi

s of

sym

met

ry

V V for all azimuth

t0 +tt0

Slower velocity

Axi

s of

sym

etry

Axi

s of

sym

etry

Anisotropy

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Anisotropy

• Well misties

• ‘Hockey stick’ effects

• Velocity variations correlating with structure

• Problems with imaging different dips

Anisotropy

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Well Mis-tie

Anisotropy

Hockey stick effects

Anisotropy

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Hockey stick effects’ corrected

Anisotropy

SURFACE-RELATED MULTIPLESpecial Processing

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Sea surface

Sea bottom

Surface-related multiple Interbed multiple

Multiples

Surface-Related Multiple Elimination

Marine data with strong surface-related multiple

Stack section after surface-related multiple elimination

Surface Related Multiple

Removing the surface-related multiple has increased the S/N ratio and made the primaries came up. It will very much help on the interpretation.

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Data contains surface-related multiple

Surface Related Multiple

Data after removing surface-related multiple

Surface Related Multiple free

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COMMON REFLECTION SURFACE

Special Processing

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(Baykulov et al., 2011)

Azimuthal processing

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Azimuthal processing

Perbandingan data di-stack dengan velocity orisinil (V-0) vs velocity baru (V-1) : Time Slice 1800ms

Stack dengan V-1Stack dengan V-0V-1 di-analisis setelah data di-rotate pada azimuth tertentu

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DEPTH IMAGINGAdvanced Processing

Time Migration Image

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Depth Migration Image

When we need Depth Migration?

S R

S R

Time Migration : retrieves the velocity profile at the CMP location and ray traces through this local 1D model, i.e. no lateral velocity variations are comprehended, the ray path is always symmetric.

Depth Migration: Velocity Model used as provided in it’s full complexity and Ray tracing comprehends velocity changes vertically and laterally. The ray path is non symmetric and summation surfaces shape becomes complex.

We need Depth Migration in subsurface that has strong lateral velocity variation. Lateral variation may be caused by faults, carbonate build-up, anticline/syncline, salt diapir, facies changing, gas pocket etc.

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Flat reflector, constant velocity model

Surface

Reflector

CMP

point

P

NMO and Stack adequate to correctly image and position point P.

Dipping reflector, constant velocity model

Surface

Reflector

CMP

point

P

Time migration will correctly image data.

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Flat reflector, laterally varying velocity model

Surface

Reflector

CMP

Point

P

- VE +VE

Requires depth migration to correctly image data.

Image position comparison

Surface

ReflectorApparent position of P on stack trace

0 offset stack trace Depth migrated trace

P

Time migrated trace

PApparent position of P on stack trace

Apparent position of P on stack trace

Image rayFull ray tracing

90

P

Normal incidence ray

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Benefit of Depth Migration

Correct vertical positioning

- if the velocity model is good enough, the image will be free of structural distortions related to lateral velocity variations that cause pull-ups and sags.

Correct lateral positioning

- if the velocity model is good enough, the events will be placed in their correct lateral position.

Improved resolution

- the image will have higher resolution than that obtained by time imaging because it doesn’t rely on the hyperbolic moveout assumption.

Allows velocity and depth estimation

- it provides it’s own diagnostics for deriving the accurate velocity model. If the depth model is correct, imaging with that model yields an identical image at all offsets/angles.

SAMPLESDepth Imaging

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Case : Fault image

PSTM section

Challenge :Fault image on the flower structure.

Case : Fault image

PSDM section

The antitetics fault now appears clearly on the flower structure by running DEPTH migration with accurate velocity model.

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Terima [email protected]

gl_seismic_dp_20140313

Documents

a0amplitude of reflected

seismic waves

reflected angle

new source of spherical

larger energy

incident amplitude

propagating seismic

unit area