Prestack explodingreflectors modeling for migration velocity analysis Biondo

Prestack exploding-reflectors modeling for migration velocity analysis Biondo Biondi – SEP 131 Prestack exploding-reflector model: the crosstalk problem Claudio Guerra and Biondo Biondi – SEP 134 May – 2008

Motivation Migration with initial velocity Migration with updated velocity WEMVA Sava and Biondi, Geophysical Prospecting, 2004 2

Goal • Synthesize a dataset to be used in velocity model update, starting from a prestack image computed with waveequation migration. • be significantly smaller (orders of magnitude) than the original dataset; and • preserve the kinematics needed to perform velocity model update. 3

Outline • • Prestack exploding-reflector model Dip-independent data Crosstalk Future work 4

Prestack exploding-reflector model offset depth time cmp cmp time migration with low velocity 5

Prestack exploding-reflector model cmp offset depth time cmp 6

Prestack exploding-reflector model depth angle Original ADCIG “Areal” ADCIG depth offset 7

Prestack exploding-reflector model • Modeling of areal sources and receivers, having a prestack wave-equation image as initial condition. • Combination of modeling experiments – data reduction 8

Dip-independent data offset depth time cmp Shot-profile migration with too low velocity 9

Dip-independent data offset depth cmp Areal-shot migration with correct velocity 10

Dip-independent data depth cmp offset ? Areal-shot migration with correct velocity 11

Dip-independent data Biondo – SEP 134 12

Dip-independent data Biondo – SEP 134 13

Dip-independent data cmp depth offset cmp offset depth cmp 14

Dip-independent data cmp depth offset cmp offset depth cmp 15

Dip-independent data cmp depth offset cmp offset depth cmp 16

Dip-independent data • In the presence of dip, data migrated with an inaccurate velocity model must be rotated according to the geological dip prior to modeling. 17

Crosstalk offset depth cmp Shot-profile migration 18

Crosstalk Modeling of areal data from 1 CIG cmp t Areal shot t Areal source 19

Crosstalk Areal shot migration of areal data from 1 CIG offset depth cmp One-way Areal shot mig. 20

Crosstalk Areal shot migration of areal data from 1 CIG offset depth cmp One-way Areal shot mig. 21

Crosstalk Modeling of areal data from 3 CIGs cmp t Areal shot t Areal source 22

Crosstalk Areal shot migration of areal data from 3 CIGs offset depth cmp One-way Areal shot mig. 23

Crosstalk Areal shot migration of areal data from 3 CIGs offset depth cmp One-way Areal shot mig. 24

Crosstalk Modeling of areal data – CIG distance 1000 m cmp t Areal shot t Areal source 25

Crosstalk Areal shot migration – maximum offset 400 m offset depth cmp One-way Areal shot mig. 26

Crosstalk Modeling of areal data – CIG distance 100 m cmp t Areal shot t Areal source 27

Crosstalk Areal shot migration – maximum offset 400 m offset depth cmp One-way Areal shot mig. 28

Crosstalk Areal shot migration – maximum offset 400 m offset depth cmp One-way Areal shot mig. 29

Crosstalk • Two distinct sources of crosstalk – exploding-reflector crosstalk • cross-correlation of events from the same CIG – reflection crosstalk • cross-correlation of events from different CIGs 30

Crosstalk attenuation • Strategies to attenuate crosstalk – Time-windowing imaging condition • Reflectors “explode” at time zero – Radom phase-encoding • decorrelate source and receiver wavefields from different experiments – a(xx, w) • decorrelate exploding reflectors – a(xx, zx, w) 31

Crosstalk attenuation Time-windowing imaging condition offset cmp offset depth cmp One-way Areal shot mig. TWIC 32

Crosstalk attenuation -random phase-encoding cmp time cmp receiver wavefield source wavefield 33

Crosstalk attenuation -random phase-encoding offset cmp offset depth cmp One-way Areal shot mig. (x, w) phase-encoding 34

Crosstalk attenuation -random phase-encoding of 4 realizations offset cmp offset depth cmp One-way Areal shot mig. (x, w) phase-encoding 35

Crosstalk attenuation -random phase-encoding of 4 realizations offset cmp offset depth cmp One-way Areal shot mig. (x, w) phase-encoding 36

Crosstalk attenuation -random phase-encoding cmp time cmp receiver wavefield source wavefield 37

Crosstalk attenuation -random phase-encoding offset cmp offset depth cmp One-way Areal shot mig. (z, x, w) phase-encoding 38

Crosstalk attenuation -random phase-encoding 4 realizations offset cmp offset depth cmp One-way Areal shot mig. (z, x, w) phase-encoding 39

Crosstalk attenuation -random phase-encoding 4 realizations offset cmp offset depth cmp One-way Areal shot mig. (z, x, w) phase-encoding 40

Crosstalk attenuation • Crosstalk of events from the same CIG can be attenuated by applying a time-windowing imaging condition; • Crosstalk of events from different CIGs can be attenuated by applying (x, w)-random phase-encoding; and • (z, x, w)-random phase-encoding has the potential to attenuate both crosstalks. 41

Future work • Modeling in a complex velocity model • Random phase-encoding – velocity errors and complex velocity models • Different imaging conditions 42