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sep:research:theses:sep166 [2016/12/08 01:40] yishen |
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==Wave-equation migration Q analysis == | ==Wave-equation migration Q analysis == | ||

- | // by Yi Shen // | + | // by [[ http://sepwww.stanford.edu/data/media/public/sep/yishen/Site/Welcome.html|Yi Shen]]// |

**Downloads** | **Downloads** | ||

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Such developed methods require highly accurate velocity models. Therefore, I also develop a multi-parameter inversion of velocity and Q models using wave-equation migration analysis. This method poses the estimation problem as an optimization problem that seeks optimum velocity and Q models by minimizing user-defined image residuals. The numerical tests on a modified SEAM model with two gas clouds demonstrate the benefit of using such multi-parameter inversion, when the existing velocity and Q models are inaccurate. The results show that this inversion method is able to retrieve both velocity and Q models, and to correct and compensate the distorted migrated image caused by inaccurate velocity and Q models. I apply this joint inversion of velocity and Q models to the 3D Dolphin’s multi-client field data acquired in the North Sea, which have attenuation and velocity problems due to shallow subsurface gas chimneys and channels that are correlated with strong attenuation and low-interval velocity. The updated velocity shows low velocity regions around the gas and channel features. The inverted Q model detects the shape and location of the gas and channel areas, which align with Dolphin’s interpretation. Consequently, the migration with the updated velocity model and the estimated Q anomalies flattens the events in the subsurface angle gathers, enhances the damped amplitudes and the frequency content of the migrated events, corrects the distorted phase of the migrated events and makes them more coherent. | Such developed methods require highly accurate velocity models. Therefore, I also develop a multi-parameter inversion of velocity and Q models using wave-equation migration analysis. This method poses the estimation problem as an optimization problem that seeks optimum velocity and Q models by minimizing user-defined image residuals. The numerical tests on a modified SEAM model with two gas clouds demonstrate the benefit of using such multi-parameter inversion, when the existing velocity and Q models are inaccurate. The results show that this inversion method is able to retrieve both velocity and Q models, and to correct and compensate the distorted migrated image caused by inaccurate velocity and Q models. I apply this joint inversion of velocity and Q models to the 3D Dolphin’s multi-client field data acquired in the North Sea, which have attenuation and velocity problems due to shallow subsurface gas chimneys and channels that are correlated with strong attenuation and low-interval velocity. The updated velocity shows low velocity regions around the gas and channel features. The inverted Q model detects the shape and location of the gas and channel areas, which align with Dolphin’s interpretation. Consequently, the migration with the updated velocity model and the estimated Q anomalies flattens the events in the subsurface angle gathers, enhances the damped amplitudes and the frequency content of the migrated events, corrects the distorted phase of the migrated events and makes them more coherent. | ||

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+ | **Reproducibility and source codes**\\ | ||

+ | This thesis has been tested for [[sep:research:reproducible|reproducibility]]. The source codes are made available for [[http://sepwww.stanford.edu/data/media/private/docs/sep166/source/source.tar.gz|download]]. The scripts for field data applications are available for [[http://sepwww.stanford.edu/data/media/private/docs/sep166/source/shScript.tar.gz|download]].\\ | ||

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+ | ** Programs for Q migration compensation and Q tomography**\\ | ||

+ | Download [[http://sepwww.stanford.edu/data/media/private/docs/sep166/source/bin.tar.gz|here]]. \\ | ||

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+ | **Defense**\\ | ||

+ | [[http://sepwww.stanford.edu/data/media/public/docs/sep166/yi_defense_clean.pdf|Defense presentation]]\\ | ||

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