Seismic data Processing

SEISMIC DATA PROCESSING  Demultiplexing  Trace

header generation

 Spherical

<…observers’ data

divergence correction

 Deconvolution

before stack

 Band

pass filter

 Trace

normalization

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SEISMIC DATA PROCESSING (contd)  Velocity  Normal  CMP

Analysis

Move Out Correction

Stack





















SEISMIC DATA PROCESSING (contd)  DMO

stack

 Random  Decon  Time

noise attenuation

after stack

Variant Filter





















Depth & Time Shot

surface

receivers 0 Layer-1

Arrival time

Layer-2 Layer-3





















Demultiplexing  Required

if the Seismic Data is recorded in multiplexed format

 Conversion

of scan sequential mode to trace

sequential mode.  Essentially

a Matrix transposition (rows to





















Multiplexing Ch-1 Ch-48

Ch-2

Ch-20

Ch-3

Ch-12

Ch-4 Ch-5























Demultiplexing Amp

SCAN-1,ch-1

SCAN-1,ch-24

SCAN-1,ch-36

SCAN-1,ch-48

SCAN-2,ch-1

SCAN-2,ch-24

SCAN-2,ch-36

SCAN-2,ch-48























T C

IO

N

S C E

T

IO

S N F E

E L

C

N IO T

S























TYPES OF NOISE  Coherent

multiples ) Noise (Ground roll, backscatter, multiples)

Methods of reduction :























NOISE SECTION First Arrivals

















































































































GATHERS OF DIFFERENT TYPES























GATHERS OF DIFFERENT TYPES





























































































































































































































































































Stack Power as a Function of Velocity And Time





















Normal Move Out Correction 

Non zero offset data is characterized by a travel time increase with increase in offset distance from the source to the reflector.



Non zero offset to zero offset conversion is achieved through a correction called as NMO (nomal move out) correction. The The NMO equation for a flat layer layer case is : Ti**2 = To**2 + Xi**2/V**2, where Ti = Travel time at offset distance Xi





















Offset 

Time









































Stacking  Each

common mid point gather after normal move out correction is summed together to yield a stacked trace.

 Stacking

enhances the in-phase components and reduces the random noise.



































































Crooked (slalom) Profile & Mid Point distribution



























































































Residual Static Corrections













































Dip Move Out Correction























Dip Move Out & Migration





























































































































































































































































































Deconvolution After Stack  NMO

correction and Stacking also act as a high cut filter. Loss of high frequencies result in loss of resolution.

 The

deconvolution employed at the post stack stage is similar to that in the pre –









































Time Variant Filter  Earth

consists of sets of layers (strata) that are distinctly characterized by certain band of frequencies.

 It

is often advantageous to view the seismic section (which is a cross section of the earth) in tune with the characteristic band of frequencies.









































Migration  When

the subsurface consists of dipping layers, the Zero offset section does not represent the cross section of the earth because the reflected energies are placed at apparent spatial locations.

 Moving

the reflection energies from the apparent locations to the true locations is achieved through ‘Migration’. The spatial velocity distribution of the























Migration A

P’

B

P























Migration







































































































































































































































































































































Seismic data Processing

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