207955295 lecture 10 sesmic data processing

8/11/2019 207955295 Lecture 10 Sesmic Data Processing

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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/



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



0

1

2

T W O W a y T i m e

Distance (Trace)Seismic section display as Wiggle+Variable area



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.



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:



Muting on actual seismic section

Dead or

badtraces

Baddataremoved



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



The importance of CDP-Stack

1-Enhancement of the signal

2- Attenuate the random noise

3- Control the multiples



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



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.



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



Coherency:It is a process by which a coherent events (Reflection signal) are enhancedand incoherent events (Wind noise) are attenuated.

Before Coherency After Coherency

207955295 lecture 10 sesmic data processing

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