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Reflection Seismic Geophysics

Marine Aqusition

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Surface Seismic Exploration Cycle

ACQUISITION

PROCESSING

INTERPRETATION

Drillhere

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2D Reconnaissance Survey 2D Detailed Survey

2D Surveys

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Source to Receiver Ray Path

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Ray Paths

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Ray Paths

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Ray Paths

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Ideal Seismogram

The seismic data recorded should give us theEarths reflectivity sequence:

Surface

Depth

Time

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Marine

Source Receiver Vessels Equipment Handling

Acquisition sequence

4C

Q

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Marine Acquisition System

Sea bed

Boat

Cable with hydrophones

Sea Surface

Source(Airguns)

Sedimentary Layers

Incident waves Reflected

waves

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Marine - Recording Equipment

Streamer

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Sea bottom

Subsurface interface

Marine Acquisition

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Common Mid Point (CMP) gather

Marine Acquisition

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Common Mid Point (CMP) gather

Primary reflections

Common Midpoint Gather

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Reflection Seismic Geophysics

Land Aqusition

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Surface Seismic Processing Sequence Step 1

Where are the shotsand receivers located?

? ? ? ? ? ?

Geometry Definition

Depth

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Surface Seismic Processing Sequence Step 3

How do we remove thenoise? Geometry Definition

Amplitude Recovery

Velocity Filtering

Offset

Time

Mud Roll500 m/s

Reflector2000 m/s

Direct wave

1500 m/s Refractor1800 m/s

Multiple< 2000 m/s

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Surface Seismic Processing Sequence Step 4

How do we improve theresolution? Geometry Definition

Amplitude Recovery

Velocity Filtering

Deconvolution

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Surface Seismic Processing Sequence Step 5

Geometry Definition

Amplitude Recovery

Velocity FilteringDeconvolution

CMP Gather

How do we order the data?

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Surface Seismic Processing Sequence Step 6

How do we correct for timedifferences due to offset within the CMP gather?

Geometry Definition

Amplitude Recovery

Velocity FilteringDeconvolution

CMP Gather

NMO Correction

Offset

Time

Time Difference

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Surface Seismic Processing Sequence Step 7

How do we get a normalincidence section? Geometry Definition

Amplitude Recovery

Velocity FilteringDeconvolution

CMP Gather

NMO Correction

CMP Stack

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Surface Seismic Processing Sequence Step 8

Geometry Definition

Amplitude Recovery

Velocity FilteringDeconvolution

CMP Gather

NMO Correction

CMP Stack

Migration

How do we get the events in theright place?

Midpoint location

Actual reflection point

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Ideal Seismogram

The recorded seismic data should give us theearths reflectivity sequence

Surface

TimeDepth

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Seismic Waves - Generation

Explosive

Vibrational

Dynamite (Land)Airguns (Marine)

Marine VibroseisLand Vibroseis

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Recording Seismic Data

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Seismic WavesSu r face Wav es

Body Waves

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Body Wave Types 2 types defined by the direction of particle motion

1. P-wavesParticle motion parallel to wave propagation

wavedirection

2. S-waves

Particle motion perpendicular to wave propagatio

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Wave Energy On land, the energy division can be as poor as:

P-wave 6%

S-wave 26%

Surface waves 68%

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Wavefronts

Wavefronts How waves actually travel Surface of equal travel time Surface of equal phase

Reflectionpoints

surface wave

RaypathsRays perpendicular to wavefrontsSimple to useRay trace modelling

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Flat Earth Primary Reflections

Source ReceiverIdeal Primaries

Trace

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Flat Earth - Primary Section

Source Receiver

Ideal PrimaryTraces

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Flat Earth - Common Mid Points

Source Receivers

3,1 4,2 5,3 6,4

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Layer Cake - Common mid-point gather

Source Receiver

Common mid-point

Ideal cmpTraces