Seeing the Invisible with Seismic Interferometry: Datuming and Migration Gerard T. Schuster, Jianhua Yu, Xiao Xiang and Jianming Sheng University of Utah

Outline Seismic Interferometry Interferometric Migration Interferometric Datuming Interferometric Tomography Conclusions

Constructive Interference Wave 1 Wave 2 = Destructive Interference Wave 1 Wave 2 eiwt eiwt + 12 = 2 - 2cos(w(t - t )) 2 1 Interferometry uses interference patterns or time differences = e iwt e -iwt 1 2 = e iw(t - t ) 12

Is the Lens Broken? Interference Pattern Optical Lens t LASER LASER Buried sources redatumed to target Interferogram only sensitive to lens geometry

Is the Lens Broken? Interference Pattern Optical Lens t LASER LASER Buried sources redatumed to target Interferogram only sensitive to lens geometry

Outline Seismic Interferometry Interferometric Migration Interferometric Datuming Interferometric Tomography Conclusions

Goal: Transform Ghost Reflections into Primary Reflection Traveltimes Uninteresting Part of Medium of Medium Time Direct LASER Greens Thm: Every Point on Surface acts as a Secondary Source Direct Ghost Ghost To Remove Kinematics of Traveling in Uninteresting Medium Time Shift Traces by Direct Times {MTBASIN

Goal: Transform Ghost Reflections into Primary Reflection Traveltimes Uninteresting Part of Medium of Medium Time Direct Greens Thm: Every Point on Surface acts as a Secondary Source Direct Ghost Ghost To Remove Kinematics of Traveling in Uninteresting Medium Time Shift Traces by Direct Times Ghost Ghost

Goal: Transform Ghost Reflections into Primary Reflection Traveltimes Uninteresting Part of Medium of Medium Time Direct Greens Thm: Every Point on Surface acts as a Secondary Source Direct Ghost To Remove Kinematics of Traveling in Uninteresting Medium Time Shift Traces by Direct Times Source Moved to Surface. Statics Eliminated

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s (g, M,s)= d( M |s)* d(g|s) s,s Every VSP source at different S reflects off M And recorded at g

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s (g, M,s)= d( M |s)* d(g|s) s,s Every VSP source at different S reflects off M And recorded at g

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s (g, M,s)= d( M |s)* d(g|s) s,s Every VSP source at different S reflects off M And recorded at g We accidentally found specular ray for given (M,g), & stationary phase says this is dominant contribution.

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s (g, M,s)= d( M |s)* d(g|s) s,s Every VSP source at different S reflects off M And recorded at g Above Datuming Formula = CSG for source at M and receiver at g

Interferometric VSP Datuming Eliminates well statics and uninteresting parts of the medium. Raise buried src to surface. (g, M,s)= d( M |s)* d(g|s) s,s

Interferometric VSP Datuming by Least Squares (g, M,s)= d( M |s)* d(g|s) s,s d = E d z 0 Data with source at depth Data with source at surface Natural extrapolation operator T [E E] E d z T -1 T 0 d = Extrapolation Deconvolution ED

Interferometric Deviated VSP Datuming Eliminates well statics and uninteresting parts of the medium. Lower surface src to well. (g, M,s)= d( M |s)* d(g|s) s,s

Interferometric CDP Datuming Eliminates src/rec statics and uninteresting parts of the medium. Lower buried src to reference inter. (g, M,s)= d( M |s)* d(g|s) s,s reference reflector reference reflector

Outline Seismic Interferometry Interferometric Migration Interferometric Datuming Interferometric Tomography Conclusions

Outline Seismic Interferometry Interferometric Migration Interferometric Datuming Interferometric Tomography Conclusions

Uninteresting Part of Medium of Medium Time Replace Time Shifting by Crosscorrelation d(M|s) d(g|s) M g s (g, M,s)= d( M |s)* d(g|s) s,s Above Formula = CSG for source at M and receiver at g’ Every surface pt at different M acts as secondary source To contribute to g Shot gather for source at M and geophone at g

Uninteresting Part of Medium of Medium Time M g s Above Formula = CSG for source at M and receiver at g’ Every surface pt at different M acts as secondary source To contribute to g (g, t + t ) (g, t + t )M g MxMxMxMx gxgxgxgx M, m(x)= X = trial image pt.

Outline Seismic Interferometry Interferometric Migration: Exxon VSP Interferometric Datuming Interferometric Tomography Conclusions

Time (s) Depth (ft) Raw Data(CRG15)

Time (s) Depth (ft) Ghosts

Depth (ft) X (ft) 0400 X (ft) Standard migXcorr. mig

Outline Seismic Interferometry Interferometric Migration: CDP Interferometric Datuming Interferometric Tomography Conclusions

Shots: 280 Shot interval: 10 m Receivers: 300 Receiver interval: 10 m Temporal interval:1ms X (km) Depth (km) Salt model

X (km) Time (s) CSG 100

X (km) Depth (km) Velocity model with inaccurate salt boundary, oceam bottom, and overburden

X (km) Depth (km) Kirmig with inaccurate salt boundary, ocean bottom, and overburden

X (km) Depth (km) RT mig with inaccurate salt boundary, ocean bottom, and overburden

X (km) Depth (km) Standard mig Correct velocity X (km) Standard mig Incorrect velocity RT mig

Summary Seismic Interferometry d(g)d(g’)* d(g) d(g’) *

Summary d(g)d(g’) * d(g) d(g’) * Time Shift = Remove Uninteresting Kinematics+Statics Kinematics+Statics DatumingMigrationTomography

Issues 1. VSP Natural Home for Interferometry 2. CDP Interferometry Eliminates statics+overburden. Widens coverage Effective if Guide Star/Reference Interface Known Less Effective if Reference not Known 3. Interferometric Datuming Naturally Datumed Data can be Filtered ID vs ED

Outline Seismic Interferometry Interferometric Migration: CDP Interferometric Datuming Interferometric Tomography Conclusions Salt Flank Imaging PS Waves

Uninteresting Part of Medium of Medium Time Goal: Image Interface by PS Transmitted Waves M g s P d(M|s) d(g|s) PPPPPPPP PSPSPSPS M g d(g|s)* (g,M) = MxMxMxMx gxgxgxgx M, m(x)= = e e i w t + i w t -i w t - i w t PSPSPSPS PPPPPPPP = e= e= e= e i w (t – t)

Uninteresting Part of Medium of Medium Time Goal: Image Interface by PS Transmitted Waves M g s P d(M|s) d(g|s) PPPPPPPP PSPSPSPS g s d(g|s)* (g,M) = MxMxMxMx gxgxgxgx M, m(x)=

Uninteresting Part of Medium of Medium Time Goal: Image Interface by PS Transmitted Waves M g s P d(M|s) d(g|s) PPPPPPPP PSPSPSPS g s d(g|s)* (g,M) = MxMxMxMx gxgxgxgx M, m(x)=

Uninteresting Part of Medium of Medium Time Goal: Image Interface by PS Transmitted Waves M g s P d(M|s) d(g|s) PPPPPPPP PSPSPSPS g s d(g|s)* (g,M) = MxMxMxMx gxgxgxgx M, m(x)= Unique Specular Point Snell’s Law OK g,M (g,M)(g,M)(g,M)(g,M) m(x) = e i w (t – t) – xxx Datuming Migration

Interferometric PS Datuming g,M (g,M)(g,M)(g,M)(g,M) m(x) = e i w (t – t) – xx Eliminates src/rec statics and uninteresting parts of the medium. Raise buried src to interesting inter.