7/29/2019 17_DMO

1/17

Loading of the data/conversion

Demultiplexing

Editing

Geometry

Amplitude correction

Frequency filter

Deconvolution

Velocity analysis

NMO/DMO-Correction

Stacking

Migration

MeasurementsNavigation

Printing/storage Printing/storage

CMP-Sorting Prestack

PoststackPost-processing

Pre-Processing

Basic scheme of the seismic data processing

7/29/2019 17_DMO

2/17

DMO (Dip move-out)

A seismic processing operation to correct for the fact

that, for dipping reflections, the traces of a CMP

gather do not involve a common reflection point.DMO effectively corrects for the reflection-point

smear that results when reflectors dip.

Events with various dips stack with the same velocity

after DMO.

(DMO can be performed in a number of ways)

Sheriff, 1991

7/29/2019 17_DMO

3/17

Horizontal Reflector

CMP = CDP

CMP CDP

Dipping Reflector

CMP = common mid pointCDP = common depth point

Dip move out (DMO)

7/29/2019 17_DMO

4/17

Loci of reflection points

Zero offset: coincident

Source (S) and geophone (G)

Common offset: offset between

Source (S) and geophone (G)

Show possible reflection points for one particular traveltime

7/29/2019 17_DMO

5/17

DMO correction

NMO:coordinate transformation from A (yn,t) to B (yn,tn)DMO:

coordinate transformation from B (yn,tn)to C (y0-t0)Zero-offset migration:

coordinate transformation from C (y0-t0)to D (ym,t)

7/29/2019 17_DMO

6/17

Dip Move out (DMO)

7/29/2019 17_DMO

7/17

Marine line over a salt structure

Cases of conflicting dip

Analysis of data without DMO correction

Analysis of data with DMO correction

(following pictures are obtained from Yilmaz, 2001)

7/29/2019 17_DMO

8/17

Selected CMP gathers from a 2D marine dataset

Yilmaz, 2001

NMO DMO NMO-1

7/29/2019 17_DMO

9/17

Velocity spectrum

Without DMO correction

(smearing of data)

With DMO correction

Yilmaz, 2001

7/29/2019 17_DMO

10/17

Close-up view of the velocity

spectrum and CMP gather

Without DMO correction

Yilmaz, 2001

7/29/2019 17_DMO

11/17

Close-up view of the velocity

spectrum and CMP gather

With DMO correction

Yilmaz, 2001

7/29/2019 17_DMO

12/17

Velocity field used to stack the CMP gathers

Without DMO correction With DMO correction

Yilmaz, 2001With DMO: less smearing: more detailed velocity field

7/29/2019 17_DMO

13/17

NMO correction of DMO corrected gathers

Without lateral varying and with lateral varying velocityYilmaz 2001

7/29/2019 17_DMO

14/17

Field example of DMO correction

NMO

Stacking

Migration

DMO NMO-1 NMO

CMP stack DMO stack

Migrated CMP stack Migrated DMO stack

7/29/2019 17_DMO

15/17

CMP stack

and

DMO stack

Yilmaz, 2001

Amplitudes of reflections

off the flanks of the salt

have similar amplitude as

flat events

7/29/2019 17_DMO

16/17

Comparison between

Migration of

CMP stack

andDMO stack

Yilmaz, 2001

Amplitudes of reflections

off the flanks of the salt

have higher amplitude

7/29/2019 17_DMO

17/17

Time migration of CMP and DMO stack

Yilmaz 2001