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Subject 10: Seismic Data Processing
Lecturer: Dr. Bakhtiar Q. Aziz
Objective: This subject is very important for BSc student so 4 hours are specified
to give the students an obvious look out about the digital sequence of essential andoptional processing. They take a flow chart of processing step by step, each processing is clarify and illustrated by diagram.Then the students will practice on which optional data is necessary for certaincases.
Scientific contents
1- Flow chart of essential data processing.
1- Flow chart of optional data processing.
3-Common depth point.
References
1. Applied and environmental geophysics, 1999, Sharma,V.,P.
2.
Introduction to geophysical prospecting, 1988, Durbin, M. B.
3. www.Geophysics.net
4. www.seismicexploration.net/
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Digital processing of seismic data
It is a sequence of operations carried out according to a predefined programto extract a useful information from a set of raw data.
It is summarized as follow:
1- Data copying.
2- data classification and storage.
3- Many types of computation and analysis.
4- Display of results.Display of raw data:
There are four types of displaying seismic data on paper:
1- Wiggles 2- Variable area 3- Wiggle+Variable area 4-Variable intensity
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0
1
2
T W O W a y T i m e
Distance (Trace)Seismic section display as Wiggle+Variable area
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Seismic Field data
True Amplitude Recovery
Data Editing
CDP Gather
Static Correction
Dynamic Correction
Muting
CDP Stack
Section Display
Vibroseis Field data
Cross Correlation
Deconvolution
Filtering
Equalazation
Migration
Coherency
Depth Conversion
Data processing Sequence
It is divide into two parts:
1- Essential Processing.
2- Optional Processing.
Optional Processing.
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True Amplitude Recovery (TAR):
Involves the removal of the following effects by multiplying the trace withthe (F
(T)Tar).
1- Spherical divergence.
2- Inelastic attenuation.
3- The net gain imposed by the recording station.
)(
..
.)(
.
...t
t v
Av
TARt
Get vC F
Av
)(
)(
t
Av
G
v
C : Scaling constant
: Average velocity
: Gain applied
: Absorption coefficientData Editing:Some seismic data is harmful on the seismic record, so they have to be removed
Such as;1- Weak data2- Dead data3- Reverse data
1-Essential Processing:
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Muting on actual seismic section
Dead or
badtraces
Baddataremoved
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SP1
SP2SP3
G1G2G3
CDP
SP1 SP2
SP3G1G2G3
CDP3-Fold, or %300, or 300 6-Fold, or %600, or 600
SP4 SP5SP6
G4G5G6
Concept of (CDP) stack
It is a process of adding all the seismic traces which return to one commondepth, it is always applied after static and dynamic corrections.
Before NMO Correction After NMO Correction After Stack
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The importance of CDP-Stack
1-Enhancement of the signal
2- Attenuate the random noise
3- Control the multiples
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CDP-Gather: After missing all unwanted data, all traces that return to one commondepth point are gathered together to examine the process of data editing
S S
S
54
CDP
S SS
321
6
1 2 3 4 5 6
Data Editing CDP-Gather
1 3 6
Muting:It is a kind of data editing by which the non-reflection events are removed, such as:1- First part of traces which contained usually refracted data, it is alsocalled (first break suppression).
2- directed waves.
Direct andRefracted events
Muting
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2-Optional processing:
Deconvolution:It is similar to TAR , but here we compensate for the loss of frequency components.This loss is caused by the effect of the earth materials that act as a filter for high
Frequency.Deconvolution also defined as a process by which we restore the observed reflectionSignal to the original form.
SP G
Frequency = 10 KHZ Frequency = 0.10 KHZ
Trace equalazation:It is a process involves the adjacent of the gain of various channels so that their Amplitudes are comparable.
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Before Equalization After Equalization
G1 G2 G3 G4 G5 G6 G7 G8 G1 G2 G3 G4 G5 G6 G7 G8
Migration:It is a process that restore the reflettion events to their proper position, it is appliedIn the following cases:1- When the dip is large.2- When there is a syncline.
Bow-Tie feature
Before migration After migration
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Coherency:It is a process by which a coherent events (Reflection signal) are enhancedand incoherent events (Wind noise) are attenuated.
Before Coherency After Coherency