Loading of the data/conversion Demultiplexing Editing Geometry Amplitude correction Frequency filter Deconvolution Velocity analysis NMO/DMO-Correction.

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

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

Horizontal Reflector

CMP = CDPCMP = CDP

CMP CDPCMP CDP

Dipping Reflector

CMP = common mid pointCDP = common depth point

Dip move out (DMO)

Loci of reflection points

Zero offset: coincidentSource (S) and geophone (G)

Common offset: offset between Source (S) and geophone (G)

Show possible reflection points for one particular traveltime

DMO correction

NMO:coordinate transformation from A (yn,t) to B (yn,tn)DMO:coordinate transformation from B (yn,tn) to C (y0-0)Zero-offset migration:coordinate transformation from C (y0-0) to D (ym,

Dip Move out (DMO)

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)

Selected CMP gathers from a 2D marine dataset

Yilmaz, 2001

NMO DMO NMO-1

Velocity spectrum

Without DMO correction(smearing of data)

With DMO correction

Yilmaz, 2001

Close-up view of the velocity spectrum and CMP gather

Without DMO correction

Yilmaz, 2001

Close-up view of the velocity spectrum and CMP gather

With DMO correctionYilmaz, 2001

Velocity field used to stack the CMP gathers

Without DMO correction With DMO correction

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

NMO correction of DMO corrected gathers

Without lateral varying and with lateral varying velocityYilmaz, 2001

Field example of DMO correction

NMO

Stacking

Migration

DMO NMO-1 NMO

CMP stack DMO stack

Migrated CMP stack Migrated DMO stack

CMP stack

and

DMO stack

Yilmaz, 2001

Amplitudes of reflectionsoff the flanks of the salt have similar amplitude as flat events

Comparison betweenMigration of CMP stack andDMO stack

Yilmaz, 2001

Amplitudes of reflectionsoff the flanks of the salt have higher amplitude

Time migration of CMP and DMO stack

Yilmaz, 2001