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Seismic Exploration
http://www.gedco.com/services/seismic/services_main.htm

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Two-dimensional Seismic Line

Seismic work is done by

introducing seismicenergy through man

made explosions

Systematic seismic lines

were laid to cover area

of interest

The survey results insubsurface profile asshown on a seismic line

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The Objective of Seismic works..

To identify exploration prospects: as part of

the prospect ranking processes

To reduce exploration risk through better

subsurface imaging techniques

The method involve the study of earthsphysical properties as waves propagation

media and its responses to artificial means

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Seismic method involves the study of

waves propagation in the earth layers

Seismic waves spread in homogenous media

The useful wave used in exploration is the P

wave The use of other waves are still in research stage

Time-distance plot is used to differentiate various

type of waves

usage

Plot T-X

Next

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Ret

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Spreading wave may cause

destructive forces.

Ret

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Next

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Ret

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Start

Seismic parameters : source,

distance and velocity

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Seismic waves inside the earth

Ret

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Ret

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Time distance plot curve

Next

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So waves retain its character by..

Its velocity of propagation

Distance from its source

Amplitude

Frequency

Phase

All of the above characters shall be the useful

tools in seismic exploration method

Next

Vel1

vel2

Vel3

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Seismic waves propagation

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Three dimensional seismic data presentation

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Wavefront and Raypath

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Wave propagation

Two layers each having

velocity of 5000 and1000 meter per second

The wave front form a

sphere while traveling

in homogenous media

At 25 ms it travels about

125 m from the source

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Head waves

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Snells Law

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Wave propagation

As the wave front reachesthe velocity interface

three waves wereformed namely: reflected,

refracted and direct wave.

The refracted wave travelscontinuously downward at

the speed of the secondlayer

Direct wave travels at aspeed of the first layer,

reaches the surface asfirst arrival

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Quiz over?

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Waves propagating in multiple layers

Three velocity layers represent seismicinterfaces

The red dot represent shot point position

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Assuming homogenous

velocity layer throughout the entire layer

The wave front travels

at a speed of 1500 m

per second

It reaches depth of

about 135 m deep after

traveling 90 ms.

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At 155 ms three waves

form interference at theboundary of layer 1 and

2

Head waves travel at the

speed of layer 2

The wave front travel

further down into layer 3

while reflected wave isabout to reach surface

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At short offset we will observe direct arrival that travel at aspeed equal with the top layer.

At intermediate offset the head wave travels at the speed ofthe second layer (B1)

At large offset head wave (B2) appears at a speed of thebottom layer.

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End of Part I

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