Slide 1

3D Tomography using Efficient Wavefront Picking of Traveltimes Abdullah AlTheyab and G. T. Schuster King Abdullah University of Science and Technology (KAUST) 1

Slide 2

Outline Introduction Areal Picking 3D Tomography using Areal Picks Conclusion 2

Slide 3

Introduction For conventional acquisition geometry, receiver lines are sparse. Picking is done on time- offset sections. first-arrivals x y t 3

Slide 4

Field Data Example 4 3D OBS data parameters: 234 OBS stations 129 source-lines 50m inline spacing 400m OBS spacing 40-50m water depth Source boat sail lines Receiver stations

Slide 5

Human picking time 30,186 sections to pick, each with 360 receivers. Estimated picking time: 2 section/minute 251hrs 8 hr/day: 31 days 5 12 km 0 3 Time [sec] CRG Shingling Low SNR

Slide 6

Quality Control and Cycle-skipping 12 km 0 3 Time [sec] Shingling Traveltime [sec] Traveltime Map 14 2 Distance [km] 1 3 Shot 73Shot 74Shot 75 6

Slide 7

Memory Footprint The size of the data is 80 GB (at 4ms sampling, after windowing). Interactive picking software require: Large memory, Swapping to hard drives. Memory access pattern for QC is complex. 7

Slide 8

Conventional Picking Approach Disadvantages: 1.Large human piking time (31 days) 2.Laborious to QC and correct picks 3.Large memory footprint (80 GB) 8

Slide 9

Outline Introduction Areal Picking 3D Tomography using Areal Picks Conclusion 9

Slide 10

Areal picking For conventional acquisition geometry, receiver lines are sparse. Picking is done on time- offset sections. first-arrivals x y t 10

Slide 11

x y t Areal picking For dense-receiver acquisition geometry We propose picking on time- slices (Areal Picking). 11

Slide 12

Areal picking For dense-receiver acquisition geometry We propose picking on time- slices (Areal Picking). y t x 12

Slide 13

Areal picking For dense-receiver acquisition geometry We propose picking on time- slices (Areal Picking). y t x 13

Slide 14

Areal picking For dense-receiver acquisition geometry We propose picking on time- slices (Areal Picking). y t x 14

Slide 15

Areal picking: Interpolation We implemented a program that does real-time interpolation. 15 Cartesian picks Polar interpolation Continuous Polygon Picks are interpolated in polar-coordinates.

Slide 16

Field Data Example 2 4 y[km] 14 x [km] 19 4 Time slice @ 0.8 sec 16

Slide 17

Field Data Example 2 4 y[km] 14 x [km] 19 4 Time slice @ 0.8 sec 17

Slide 18

Field Data Example y[km] 14 x [km] 19 4 Time slice @ 2.4 sec 18

Slide 19

Field Data Example y[km] 14 x [km] 19 4 Time slice @ 2.4 sec 19

Slide 20

Field Data Example: Human picking time 20 200 ms time-slice spacing for 5 Hz FWI. 234 shots x 15 slices/shot= 3,510 slices (vs. 30,186 sections) to pick. Estimated picking-time: @2 slices/minute: 30 hrs @8 hr/day: 4 days (vs. 31 days)

Slide 21

Field Data Example: Quality Control Polygon must not cross. y[km] 14 x [km] 19 4 Time slice @ 2.4 sec 21

Slide 22

Field Data Example: Quality Control Min Apparent velocity Max 22 Detect mispicks. Apparent Velocity Map Explore regional trend

Slide 23

Field Data Example: Memory footprint 80 GB Slicing for 5Hz FWI 2 GB Slices are spaced at of the shortest period. 23

Slide 24

Outline Introduction Areal Picking 3D Tomography using Areal Picks Conclusion 24

Slide 25

Polygon resampling y[km] 14 x [km] 19 4 Picked Traveltime Map Regularized Traveltime Tomography 0 3 Traveltime [sec] 25

Slide 26

Tomography using Areal Picks y[km] 14 x [km] 19 4 Picked Traveltime Residual Regularized Traveltime Tomography -0.1 0.1 Residuals [sec] 26

Slide 27

Tomography using Areal Picks Cycle skipping Count Traveltime Error [sec] -0.50.10.5-0.10 Traveltime Error Histogram 27

Slide 28

Final Traveltime Tomogram 28 0 3.5 10 depth slice x [km] y [km] 10 inline xline 0 z [km] y [km] 0 15004500 Velocity [m/s] 018 Structural cross-section

Slide 29

Field Data Example: Waveform Comparison 29 12 km 0 3 Time [sec] Observed

Slide 30

Field Data Example: Waveform Comparison 30 12 km 0 3 Time [sec] Calculated

Slide 31

Field Data Example: Waveform Comparison 31 12 km 0 3 Time [sec] Observed

Slide 32

Field Data Example: Waveform Comparison 32 12 km 0 3 Time [sec] Calculated

Slide 33

Field Data Example: Waveform Comparison 33 12 km 0 3 Time [sec] Observed

Slide 34

Field Data Example: Waveform comparison 34 12 km 0 3 Time [sec] Calculated

Slide 35

Field Data Example: Waveform Comparison 35 12 km 0 3 Time [sec] Observed

Slide 36

Field Data Example: Waveform Comparison 36 12 km 0 3 Time [sec] Calculated

Slide 37

Outline Introduction Areal Picking 3D Tomography using Areal Picks Conclusion 37

Slide 38

Conclusions Areal picking allows for building 3D tomograms in reasonable time. Advantages of areal picking: About 70-90% reduction in human picking time (31 vs. 4 days) Easier QC and correct mispicks Much lower memory footprint (80 GB vs. 2 GB) 38

Slide 39

Thank you Acknowledgments: Pemex for providing the data. Sponsors of CSIM Saudi Aramco for supporting the FWI project. Research Computing at KAUST. 39