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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3D CONSTRAINED LEAST-SQUARES KIRCHHOFF PRESTACK TIME MIGRATION Alejandro Cabrales Vargas
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi OUTLINE MOTIVATION WHAT CLSM CAN DO WHAT CLSM CANNOT DO IMPLEMENTATION OF CLSM NUMERICAL EXAMPLES: RESULTS IN 2D NUMERICAL EXAMPLES: PRELIMINAR RESULTS IN 3D TO DO CONCLUSIONS AKNOWLEGEMENTS
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Kirchhoff algorithm is an economical and extensively used technique to perform 3D prestack-time migration. However, coarse sampled data generates acquisition footprint and aliasing artifacts, which seriously interfere with the interpretation of shallow targets. They negatively affect prestack techniques like AVO and elastic inversion. Irregular sampling makes difficult and ambiguous the velocity analysis. Can constrained least-squares migration (CLSM) be used to reduce these artifacts and improve the seismic amplitudes? MOTIVATION
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Here we can observe the impact of the acquisition footprint in seismic interpretation. Taken form Falconer and Marfurt (2008) MOTIVATION
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi WHAT CLSM CAN DO Reduce aliasing artifacts caused by coarse and/or irregular sampling in the acquisition geometry. Improve seismic amplitudes in prestack migrated data (e.g. CIG), what makes AVO results more reliable. Predict missing traces in the data. This allows a better velocity analysis, e.g. for depth migration. Due to the flexibility in the choice of the constraint function, CLSM can be adapted to solving a specific problem.
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi WHAT CLSM CANNOT DO Cannot predict unrecorded seismic events. Cannot fix inaccuracies in the velocity field. The CLSM method assumes the velocities are correct. Generally it cannot eliminate stretch (we still have to mute). Cannot always improve the final migrated stack image. Stacking is a very powerful filter.
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi IMPLEMENTATION OF CLSM Theory relates seismic data to Earth’s reflectivity. We control the quality of the synthetic data! MODELING: d = Gm E.T. Salt model
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi IMPLEMENTATION OF CLSM We want to revert the process. But in real life, seismic data is not perfectly acquired… … so in the final migrated gathers, the image is severely affected! Common image gatherCommon offset gather IRREGULAR ACQUISITION MIGRATION: m’ ≈ G T d
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi IMPLEMENTATION OF CLSM … and to improve the quality of the migrated gathers! Common offset gatherCommon image gather But we may use constrained least-squares migration to interpolate missing traces… CLSM: PREDICT MISSING TRACES CLSM: [G T G]m lsq ≈ G T d
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi IMPLEMENTATION OF CLSM Final stack, conventional migration Final stack, CLSM However, stacking attenuates the aliasing noise, so migrated stack images are very similar.
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi NUMERICAL RESULTS IN 2D
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi I test conventional Kirchhoff migration and CLSM in the anisotropic version of Marmousi (Alkalifah, 1997) and in the Hess Corporation’s VTI datasets (available at the SEG software website). Nevertheless, I am not currently testing anisotropy. I generate aliasing artifacts by killing about 2/3 of the traces in the datasets to simulate a severe 3D irregular acquisition. I compare the original data with the predicted data obtained by conventional migration and CLSM. I compare representative near-offset sections, common-image gathers (CIG) and the full stack sections after conventional migration and CLSM. 2D WORKFLOW
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi MARMOUSI MODEL
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers before killing traces MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers after killing traces MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers predicted with conventional migration MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers predicted with CLSM (5 iter.) MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers before killing traces MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3rd nearest offset Prestack Kirchhoff migration MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3rd nearest offset Prestack CLSM (5 iter.) 3rd nearest offset MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 300th CIG Prestack Kirchhoff migration MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 300th CIG Prestack CLSM (5 iter.) MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack conventional migration MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack CLSM (5 iter.) MARMOUSI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi HESS VTI MODEL
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers before killing traces HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers after killing traces HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers predicted with conventional migration HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers predicted with CLSM (5 iter.) HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Common-shot gathers before killing traces HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3rd nearest offset Prestack Kirchhoff migration HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3rd nearest offset Prestack CLSM (5 iter.) HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 1500th CIG Prestack Kirchhoff migration HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 1500th CIG Prestack CLSM (5 iter.) HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack Kirchhoff migration HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack CLSM (5 iter.) HESS VTI
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi PRELIMINAR RESULTS IN 3D
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi I tested conventional migration in the Dickman 3D data set. I decimated the data in time (from 2 to 4 ms) and used every two input traces. I cropped the volume in time, using just the first 1.2 s. Decimation apparently enhanced acquisition footprint. The 3D version of the CLSM algorithm still is in debugging. 3D WORKFLOW
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack Kirchhoff migration Crossline 60
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Full stack Prestack Kirchhoff migration Inline 60
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Timeslice 0.964 s
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Timeslice 0.7 s
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi Timeslice 0.436 s
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi TO DO Final minor debugging in 2D CLSM algorithm. Major debugging in 3D CLSM algorithm. Memory management in 3D CLSM (MPI parallelization). Incorporation of SEP libraries in the codes (give up working with ASCII files!). Optimization of the constraint function in 3D CLSM.
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi CONCLUSIONS
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 2D CONCLUSIONS CLSM can reconstruct missing traces in an irregularly sampled dataset. CLSM attenuates aliasing noise due to coarse sampling in CO sections and CIG. Most aliasing noise is attenuated by stacking. Hence, CLSM and conventional Kirchhoff migration stacked sections are similar. CLSM requires migration and modeling at each iteration, thereby increasing the cost. However, AVO, velocity analysis and other prestack processes can be greatly improved.
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi 3D PRELIMINAR CONCLUSIONS 3D Kirchhoff migration algorithm shows sensible performance when tested in the Dickman dataset. Amplitude preservation has to be included in the code. Acquisition footprint in the Dickman migrated volume constitutes the main challenge for the 3D CLSM algorithm!
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Attribute- Assisted Seismic Processing and Interpretation http://geology.ou.edu/aaspi AKNOWLEDGEMENTS Thanks to Dr. Marfurt, Dr. Tim and Dr. Keller, my committee members. Thanks to the Pemex E&P crew for their support (mainly economical!) Thanks to quasi-Dr. Kui Zhang and quasi-Dr. Bo Zhang and all my friends. Thanks to “Tio Sergio”, for being here and for many years of advice! And of course, thanks for your attention!
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