Advances in velocity model-building technology for subsalt imaging

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE173-VE181 ◽  
Author(s):  
Bin Wang ◽  
Young Kim ◽  
Chuck Mason ◽  
Xiansong Zeng
Keyword(s):  
Model Building ◽  
Seismic Energy ◽  
Velocity Model ◽  
Hydrocarbon Exploration ◽  
Building Technology ◽  
Depth Processing ◽  
Velocity Model Building ◽  
Formidable Challenge ◽  
Subsalt Imaging

Seismic imaging of hydrocarbon accumulations below salt is a formidable challenge because complexly shaped salt bodies severely distort wavefronts or scatter seismic energy. We have highlighted some recent advances in building a velocity model for subsalt imaging. There are three main stages: suprasalt velocity determination, salt-model definition, and subsalt velocity update. Volumetric high-resolution tomography that incorporates high-velocity contrast boundaries is used to derive a good sediment velocity model before building a salt model. To facilitate integration of interpretation and depth processing, beam-based interactive imaging is used to refine the salt geometry. For subsalt velocity update, either subsalt tomography or subsalt scan-based techniques can be used, depending on the quality of subsalt reflections. There are concepts and techniques for attaining subsalt images suitable for hydrocarbon exploration beneath complexly shaped salt bodies.

Salt interpretation enabled by reverse-time migration

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE211-VE216 ◽  
Author(s):  
Jacobus Buur ◽  
Thomas Kühnel
Keyword(s):  
Model Building ◽  
Velocity Model ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Seismic Line ◽  
Depth Migration ◽  
Time Migration ◽  
Velocity Model Building ◽  
Migration Method

Many production targets in greenfield exploration are found in salt provinces, which have highly complex structures as a result of salt formation over geologic time. Difficult geologic settings, steep dips, and other wave-propagation effects make reverse-time migration (RTM) the migration method of choice, rather than Kirchhoff migration or other (by definition approximate) one-way equation methods. Imaging of the subsurface using any depth-migration algorithm can be done successfully only when the quality of the prior velocity model is sufficient. The (velocity) model-building loop is an iterative procedure for improving the velocity model. This is done by obtaining certain measurements (residual moveout) on image gathers generated during the migration procedure; those measurements then are input into tomographic updating. Commonly RTM is applied around salt bodies, where building the velocity model fails essentially because tomography is ray-trace based. Our idea is to apply RTM directly inside the model-building loop but to do so without using the image gathers. Although the process is costly, we migrate the full frequency content of the data to create a high-quality stack. This enhances the interpretation of top and bottom salt significantly and enables us to include the resulting salt geometry in the velocity model properly. We demonstrate our idea on a 2D West Africa seismic line. After several model-building iterations, the result is a dramatically improved velocity model. With such a good model as input, the final RTM confirms the geometry of the salt bodies and basically the salt interpretation, and yields a compelling image of the subsurface.

scholarly journals Automatic Velocity Model Building Technology

2010 ◽  
Vol 2010 (1) ◽  
pp. 1-1
Author(s):  
Sun Kaifeng ◽  
Wu Peng ◽  
Yang Qinyong
Keyword(s):  
Model Building ◽  
Velocity Model ◽  
Building Technology ◽  
Velocity Model Building

scholarly journals Selected aspects of modern seismic imaging and near-surface velocity model building in the area of Carpathian fold and thrust belt

2021 ◽  
Vol 47 (2) ◽  
Author(s):  
Andrzej Michał Dalętka
Keyword(s):  
Model Building ◽  
Geophysical Methods ◽  
Velocity Model ◽  
Hydrocarbon Exploration ◽  
Surface Velocity ◽  
Structural Representation ◽  
Near Surface ◽  
Velocity Model Building ◽  
Orogenic Wedge ◽  
Refraction Tomography

Despite the increasing technological level of the reflection seismic method, the imaging of fold and thrust belts remains a demanding task, and usually leaves some questions regarding the dips, the shape of the subthrust structures or the most correct approach to velocity model building. There is no straightforward method that can provide structural representation of the near-surface geological boundaries and their velocities. The in-terpretation of refracted waves frequently remains the only available technique that may be used for this purpose, although one must be aware of its limitations which appear in the complex geological settings. In the presented study, the analysis of velocity values obtained in the shallow part of Carpathian orogenic wedge by means of various geophysical methods was carried out. It revealed the lack of consistency between the results of 3D refraction tomography and both the sonic log and uphole velocities. For that reason, instead of the indus-try-standard utilization of tomography, a novel, geologically-consistent method of velocity model building is pro-posed. In the near-surface part, the uphole velocities are assigned to the formations, documented by the surface geologic map. Interpreted time-domain horizons, supplemented by main thrusts, are used to make the velocity field fully-compatible with the litho-stratigraphic units of the Carpathians. The author demonstrates a retrospective overview of seismic data imaging in the area of the Polish Carpathian orogenic wedge and discusses the most recent global innovations in seismic methodology which are the key to successful hydrocarbon exploration in fold and thrust regions.

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