Seismic Migration

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Seismic Migration:

Seismic Migration Seismic Reflection By : Muhammed hussain tajuddin

Content:

Content Background information - Seismic data processing Seismic Migration - What is Seismic Migration? - When is it used? - Types of Migration - Migration methods

- Seismic data processing:

- Seismic data processing 1-Lienear Noise Attenuation. 2-Normal move out 3-Stacking. 4-Velocity analysis. 5-Static correction. 6-Migration

Seismic Migration:

Seismic Migration Migration –Moving from one place to another What is Seismic Migration? - A data-processing technique . - An image of earth structure. - A seismic reflection survey.

What Migration do:

What Migration do Before migration After migration

SEISMIC MIGRATION is applied in two cases ::

SEISMIC MIGRATION is applied in two cases : Presence of Inclined Surface Reposition of displaced reflections that were displaced because of dip Existing of Diffracting points Remove diffraction images that may (may not) superimpose on reflections

Presence of Inclined Surface:

Presence of Inclined Surface True reflector Displaced image Of reflector

Slide 9:

Incorrect reflector Image Correct reflector image

We need the following to displace the reflecting point to its correct position ::

We need the following to displace the reflecting point to its correct position : 1- dip angle ( ) 2- the horizontal distance (X) Apparent dip angle ( ) is given by tan  = z ’ /x True dip angle is ( ) given by sin  = z ’ /x Depth of reflecting point (z ’ ) = V 1 (t o1 -t o2 ) = V 1 t  = sin -1 (V 1 t/x) z = V 1 t o cos  x = V 1 t o sin 

Existing of Diffracting points:

Existing of Diffracting points Travel paths of waves diffracted from point Q on a reflector with a vertical offset Point Q behaves as secondary source called a diffractor . Waves from the Diffractor are received at every receiver.

Migration in anticlines and synclines:

Migration in anticlines and synclines Synclines produce a bow-tie Anticlines broaden

MODEL:

MODEL Comparative Effects of 2D & 3D Seismic Data Migration

Types of Seismic Migration:

Types of Seismic Migration 1-Time migration : The geometrical relationships between seismic events on the time section.

Slide 15:

2- Depth migration : generates a true depth section. Necessary when strong lateral velocity gradients .

Migration methods:

Migration methods - PRE-STACK MIGRATION - POST-STACK MIGRATION

PRE-STACK MIGRATION ::

PRE-STACK MIGRATION : Migrate data before stacking sequence occurs. Pre-stack depth migration (PDM) Require more knowledge about subsurface velocity structure. Better results

POST-STACK MIGRATION ::

POST-STACK MIGRATION : Seismic data is migrated after stacking sequence occurs. Basis: All data elements -Primary Reflections -Diffractions

3-D post-stack time migration:

3-D post-stack time migration

3-D pre-stack depth migration:

3-D pre-stack depth migration

Unmigrated seismic section :

Unmigrated seismic section

migrated seismic section :

migrated seismic section

Thank you