Salt Flank Delineation by Interferometric Imaging of Transmitted P-to-S Waves Xiang Xiao Advisor: Gerard T. Schuster Committee: Michael Zhdanov Bob Smith Cari Jonson Univ. of Utah Nov. 15 MS thesis

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

I. Motivation Goal: –Salt Flank Imaging with Migration of Transmitted P-to-S Waves; Method: –Standard Migration (KM); –Reduced-time Migration (RM), Sheley and Schuster, 2003; –Interferometric Migration (IM), and Interferometric Redatuming (IR), Schuster, 2004;

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

Goal: Image Interface by PS Transmitted Waves M g Uninteresting Part of Medium of Medium sTime P d(M|s) d(g|s) PPPPPPPP PSPSPSPS X e i w (t + t) – w,s,M m(x) = d(M|s) sx xMxMxMxM Standard Kirchhoff Migration:

Goal: Image Interface by PS Transmitted Waves M g Uninteresting Part of Medium of Medium sTime P d(M|s) d(g|s) PPPPPPPP PSPSPSPS X Reduced-time migration: e i w (t + t + t) – w,s,M m(x) = d(M|s) sx xMxMxMxMerror ~( t + t )- ( t + t ) sx xgxgxgxgpickpicksx xgxgxgxg error t sx xMxMxMxM =( t + t )- ( t + t ) pickpicksx xMxMxMxM

Goal: Image Interface by PS Transmitted Waves M g Uninteresting Part of Medium of Medium sTime P d(M|s) d(g|s) PPPPPPPP PSPSPSPS d(g|s)* (g,M) = ~ e e i w t + i w t -i w t - i w t PSPSPSPS PPPPPPPP = e= e= e= e i w (t – t) Interferometric migration:

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

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

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

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. Move surface src to interesting inter.

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

III. Numerical Tests I.Rugose Lower Salt Boundary II.Elastic Salt Model

Salt Velocity Model Salt S-wave Velocity ModelSalt P-wave Velocity Model Depth (m) X (m) m/s III. Numerical test P-to-S ratios =

VSP Gathers Time (s) PS Waves (0,0) Time (s) P Wave (0,0) Depth (m) III. Numerical test

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. Move surface src to interesting inter.

Synthetic vs. Redatuming Data Time (s) S-P Data from IR Time (s) Synthetic S-P SWI Data Depth (m) III. Numerical test

KM vs. IM with Correct Velocity Model IM KM Depth (m) X (m) III. Numerical test E 4 -8E 4

KM, RM vs. IM Constant Static Shift in Data Each Trace Advances 8 ms III. Numerical test

KM Depth (m) X (m) Incorrectly imaged Boundary is shifted III. Numerical test

RM Depth (m) X (m) Correctly imaged Poor focused III. Numerical test

IM Depth (m) X (m) E 4 -8E 4 Correctly imaged Strong focused! Small cover of PS ray Additionally imaged III. Numerical test

Comparison Depth (m) X (m) KM RM IM III. Numerical test

Incorrect Migration Model KM, RM vs. IM 90% Velocity Above Salt III. Numerical test

KM Depth (m) X (m) Correct place Incorrectly imaged III. Numerical test

RM Depth (m) X (m) Incorrectly imaged, Should image as black boundary Correctly imaged III. Numerical test Elliptical artifacts

IM Depth (m) X (m) E 4 -6E 4 Correctly imaged Correctly imaged! III. Numerical test Elliptical artifacts are removed

Comparison KM RM IM Depth (m) X (m) III. Numerical test

II. Elastic Salt Model

P-wave velocity model 0 Depth (m) X (m) Velocity (m/s) Gas target lower boundary

a) P-wave velocity modelb) S-wave velocity model 0 Depth (m) X (m) X (m) 0 Depth (m) c) CRG 1 X-componentd) CRG 1 Z-component Shot number Time (s) Shot number Time (s)

a) Ray tracing: direct Pb) Ray tracing: PPS events 0 Depth (km) X (km) 016X (km) 0 Depth (km) 11 c) Ray tracing: PSS events 0 Depth (km) X (km)

a) PP Standard Migrationb) PS Standard Migration 0 Depth (m) X (m) c) Zoom View of PS KMd) Zoom View of PS IM X (m) X (m) 0 Depth (m) Depth (m) X (m) Depth (m)

PS IM PS interferometric migration X (m) Depth (m) Correctly imaged!

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

IV. Field Data Depth (m) X (m) Offset (m) Well and Source Location m offset

P-to-S ratios = 2.7 Velocity Profile S Wave P Wave Depth (m) Velocity (m/s) m 3200 m Salt IV. Field Data Incorrect velocity model P-to-S ratios = 1.6

150 Z Component Depth (m) Traveltime (s) Salt Direct P Reflect P Alias (Reverberation) IV. Field Data

150 X Component Depth (m) Traveltime (s) Salt Direct P Reflect P Alias (Reverberation)Direct S IV. Field Data

Processing Flow Chart Original Data Reoriented Pick desired events Flatten, median filter, unflatten Migration (KM, RM, IM)

Depth (m) Traveltime (s) IV. Field Data 150 X Before Rotation

Depth (m) Traveltime (s) IV. Field Data 150 X After Rotation P wave energy was maximized

Depth (m) Traveltime (s) III. Field Data 150 X PSS Events Transmitted at upper boundary

150 X PPS Events Depth (m) Traveltime (s) III. Field Data Transmitted at lower boundary

Migration of PSS IV. Field Data Ray Path Coverage Depth (m) SALT Offset (m)

Migration of PSS IV. Field Data SALT 150 offset RM150 offset IM Offset (m) 150 offset KM Depth (m)

Ray Path Coverage Depth (m) Migration of PPS IV. Field Data SALT Offset (m)

IV. Field Data Migration of PPS SALT 150 offset RM150 offset IM offset KM Depth (m) Offset (m)

Outline I.Motivation II.Theory III.Numerical Tests IV.Field Data Examples V.Conclusion

IV. Conclusion Advantage of PS transmission migration –it is capable of illuminating the boundary of salt flanks above the receivers (and nearly vertical boundaries if they exist).

IV. Conclusion Benefits of IM: –Remove influence of static shifts and/or migration velocity errors; –Eliminated source statics by correlation; –Accurately image the salt boundary above the receivers; Drawbacks of IM: –Migration artifacts due to violation of stationary phase approximation; –Extra summations and computation time; –Small range of incidence angle than true SWI data; –Worse spatial resolution than KM; –Does not require knowledge of the overburden velocity;

V. Future Work Pp/Ps reflection interferometric migration Anisotropy migration –Try different VTI FD synthetic walkaway VSP data set; –Apply it to a real data set; Preprocessing: –Reorientation, separation, filtering, statics correction Postprocessing: –Deconvolution Potential application –Kirchhoff multi arrival migration –Subsalt imaging –Interferometric tomography

Thanks to Jerry Schuster and my committee members: Dr. Michael Zhdanov, Dr. Bob smith, Dr. Cari Johnson for their advice and constructive criticism; Scott Leaney and Hornby Brian for their help on modeling;

Thanks to UTAM friends: –Jianhua Yu for his help on Linux programming; –Jianming Sheng and Min Zhou for their experiences on interferometric imaging; –Zhiyong Jiang and Ruiqing He for their help on classes; –Travis Crosby and all UTAM students for their cheerful attitude; All UTAM sponsors for their support; Family –My parents, brother and sister; Friends –Liyun Ma, Huajian Yao, Zhaoyu Luo and Meiping Tong, who encouraged me to continue on with my research.

Questions?