westerngeco presentation - seismic data processing

Simple Seismic Data Processing WorkflowCompiled by :

Hatem Refaat Abdel Mobdy RadwanSenior Geophysics Student

Faculty of Science, Ain Shams university.

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Activities-Affiliations:- Active Member in The Society of Exploration Geophysicists Student Chapter "SEG" since july 2014. - Active Member (MENTOR) in “SPWLA” Ain Shams University Student Chapter Since October 2015.

-Volunteering Experience: - Formal volunteer at Egyptian food bank 2010-2012.

Personal Introduction

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Hatem Refaat Abdel Mobdy - Simple processing sequence

Field Data Input

Geometry Update

Trace Editing

Amplitude Recovery

Noise Attenuation

Deconvolution

CMP sorting

NMO Correction

Demultiple

Stretch Mute

Migration

Stacking

Post Stack Sequence

Simple Processing Workflow overview

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Field Data InputRaw field Data must be reformatted into the company internal format (software format).

Usually the raw field data comes with SEG-D Format !!

Field data formatSEG YSEG D

Internal format of SLB Omega (DIO)

Internal format is usually more efficient and reduces data size by 40%

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Geometry UpdateUpdate the X,Y coordinates, elevation, line & point numbering, source & receiver types, shooting pattern information by merge the Navigation/SPS file with the data file header .

Elevation map

78 ft

117 ft

Fold Map

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Trace Edit

Aim:1- Remove bad traces(very noisy traces).2- Remove bad shots.3- Edit Polarity Reversed traces.

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Trace Edit

Before AfterN.B:AAA filter can easily attenuate these noise without killing the traces.

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Amplitude RecoveryAim:Compensate the effect of Trace amplitude decay, There are 3 main causes of attenuation(decay)

Geometric attenuation Absorption Transmission

Before After

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Noise Attenuation: Ground RollGenerated by: surface waves

Characterized by: low velocity, low frequency, high amplitude

Can be attenuated using: f-k filter, radon transform, wavelet transform, curvelet transform

BeforeAfter

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Noise Attenuation: Seismic interference(SI)

Caused by interference with another seismic survey in the same time in the same area

can be attenuated by Tau-p mutes that isolate the (SI) in Tau-p domain

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Deconvolution (Decon)Decon is an inverse filter that used to improve seismic resolution by removing the adverse filtering effects encountered by Seismic Waves during their passage through the earth (which acts as a filter).

After Before

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CMP sortingData sorting is re-organising (reordering) the data, to perform a certain process.CMP sorting performed in order to perform Velocity analysis to determine the stacking velocity.

CVSSemblanceCMPs in offset

planes

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Normal Move Out Correction (NMO)NMO Correction uses the stacking velocity which is determined by velocity analysis to remove the NMO effect.NMO effect increase with offset, decrease with time, depth and velocity.

(a) Event isn’t corrected(b) Event correct with proper velocity(c) Event is over-corrected (velocity is

too low)(d) Event is under-corrected (velocity

is too high)

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Stretch MuteEvent after NMO correction, First arrivals stretch and become low frequency these two effects increase with offset

(occur at the far offset).

MuteCMP gather NMO

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Demultiple

Multiples cause by: multiple reflections of the primary wave.

Can be attenuated by: f-k filter, Tau-p filter, stacking, Deconvolution.

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Demultiple

Can be attenuated by: f-k filter, Tau-p filter, stacking, Deconvolution.

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MigrationReposition the reflection points from their apparent location to their true location (in case of dipping reflectors and complex structures)

Increasing structure

complicity

Increasing lateral

velocity complicity

Post stack Time Migration

Post stack Depth Migration

Pre-stack Time MigrationPre-stack Depth

Migration

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Pre-stack Migration

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Post stack Migration

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Stacking

Stacking is basically a summation process, summing the traces to produce a stacked section represent the subsurface.

Stacking depend on many factors, but the most important factor is the stacking velocity (determined by Velocity Analysis)

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Post Stack sequence

Filtering:After stacking, filtering can remove high and low frequency noise !

Amplitude scaling: Acquire the final section a suitable amount of gain for better interpretation.

Final product:Ask client for final product list to deliver in SEGY format.

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Thank You !

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Any Questions ?!

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