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Research Collection

Educational Material

Reflection seismic 1 script

Author(s):

Kruk, Jan van der Publication Date:

2001

Permanent Link:

https://doi.org/10.3929/ethz-a-004363847

Rights / License:

In Copyright - Non-Commercial Use Permitted

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use.

ETH Library

(2)

Seismische Mess-Systeme

Land Marine

(3)

Source Receiver

Computer

Seismic waves

(4)

Important properties:

• Energy

• Waveform

• Repeatability

• Cost and use in the field

(5)
(6)

Impulsive source/Non impulsive source Explosive source/Non explosive source Advantages/disadvantages

(7)

Dynamite (explosive impulsive source):

• 40% of the seismic measurements

• Not really repeatable

• Exact time of detonation is difficult to obtain

• Detonators are sometimes used for shallow applications

• High energy

• For each application the amount of dynamite can be adjusted

dynamite

Trigger cable

(8)
(9)
(10)

Shear wave hammer

(11)
(12)

Vibroseis truck

(13)

Reynolds, 1997

(14)
(15)
(16)

Damping factor h

(17)

α

Apparent velocity:

sinα v

app

= v

f v

app

app

=

λ

Apparent wavelength:

= v

app

=

λ

app

= v v

app

f

= v

λ

app

(18)

( )

β

sin

) (nβ

= sin

Response function: R

where:

app

x

λ β = π

And n is the number of geophones in a group

(19)

apparent

(20)

Clustered geophones Geophone arrays

(21)

PGS J.W. Schoolmeesters

(22)

Chirp

(23)

Boomer

(Huntec-systems)

(24)

Principle of an Airgun

(Bolt-Systems)

(25)

Inside of an airgun

(Bolt-Systems)

(26)
(27)
(28)

One air gun Array of air guns

(29)
(30)

Principle of piezoelectric effect

Voltage proportional to the variation of the pressure

(31)

Acquisition Techniques

Ocean Bottom Cable

Streamer

Vertical Cable Dragged Array Anchored Cable

PGS J.W. Schoolmeesters

(32)
(33)

PGS J.W. Schoolmeesters

(34)
(35)
(36)
(37)

Multi-channel seismic recording system

(38)

(Kearey and Brooks, 1991)

sampling

Registration of the measured data at certain time intervals

Sampling interval t sampling rate 1/t

Sampling will preserve all frequencies up to the Nyquist frequency:

fN=1/(2 t)

(39)

Aliasing

(Kearey and Brooks, 1991)

Nyquist Frequency:

fNy 1 2--- 1

t ---

=

Typical sampling distances:

0.25,0.5 ms:

High resolution seismic 1 ms, 2 ms

Oil exploration 4 ms or larger

Crust seismic

(40)

Range which can be measured using different number of bits:

8-bit : 1 mV - 256 mV 24-bit: 1 µV - 16 V

Dynamic range is expressed in dB,

Examples:

÷ø ç ö

è æ

min

log max

20 A

A

dB 1mV 48

256mV log

20 ÷ =

ø ç ö

è æ

dB V 144

1 log 16V

20 =

÷÷øö ççèæ

µ

(41)

mV

2 1 8 4

16 32

64 128

Analog Signal 53

Working of an AD-converter

1 0 1 0 1 1 0 0

= 1+..+4+..+16+32+..+..

(42)

Saving requirements depend on:

Number of channels

Number of values per channel

(Sampling rate,Time window of sampling)

Number of bytes per sampled value

Example Channels: 96

Sampling rate: 2 ms Time window: 0.8 s

Format: 4 Bytes per value

Þ (800 / 2) Values x 96 channels x 4 Bytes = 0.146 MBytes

Saving requirements

Referenzen

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This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection.. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms