## Computational & Experimental Geophysics

Seismic & Acoustic Imaging

Seismic & Acoustic Imaging

The Imaging Team conducts basic and applied research in wave propagation, seismic imaging, scattering, and the interaction of acoustic waves with rock mass structure, fabric, and pore fluids, and medical imaging. We are developing and testing a wide range of new methods for rapid modeling of seismic wave propagation and for obtaining improved seismic images of the Earth's subsurface, using seismic migration in regions of geological complexity. For more information, visit our Next-Generation Seismic Modeling and Imaging site or contact Jim Tencate or Paul Johnson, or Lianjie Huang.

3-D Imaging & ModelingIn each of our three imaging and modeling projects, we are developing new methods, implementing them on parallel computers, and investigating the range of applicability of the methods by doing tests on synthetic (numerical) and field datasets. All three projects are collaborative studies with the petroleum industry. Image - Seismic images from model of the earth containing a salt body (SEG-EAEG salt model). Top image obtained with state-of-the-art wave-equation-based imaging developed at Los Alamos. Bottom image obtained with conventional ray-based imaging method. |

3-D ModelingOur 3-D modeling project is focused on the evaluation of elastic and anisotropic wave propagation effects. Modeling results are being used to test imaging and other seismic processing methods. These methods conventionally are done with the assumption that the earth is acoustic (capable of transmitting only compressional waves). Images - Wave snapshots from model calculations of a simple layer over halfspace structure. Top plot includes compressional waves (reds). Bottom plot includes compressional (reds) and shear waves (greens). Images courtesy of Shawn Larsen, Lawrence Livermore. |

**Next-Generation Seismic Modeling and Imaging**

The project aims to improve 3-D seismic modeling and imaging. Through collaboration with oil and gas industry participants, appropriate 3-D elastic models will be designed and built for the numerical modeling efforts. These models will be provide challenging tests of 3-D imaging, as well as calibration of processing routines. New 3-D imaging methods will be developed and tested and compared to available methods. The project aims to reduce the financial and environmental costs of exploring and producing oil and gas.

This effort is a collaboration between SEG (through a subcommittee of the SEG Research Committee) and the U.S. Department of Energy (through the National Gas and Oil Technology Partnership) and national laboratories and universities. The U.S. Department of Energy provides funding for the national laboratory participants, and much of the funding for the university participants. The industry participants fund their own time, and provide in-kind contributions to the project.

As industry searches for new oil and gas sources in ever more complex geologic structures, accurate and reliable seismic imaging is increasingly important. These complex geological structures can be very difficult to image properly, and conventional 3-D imaging methods often provide poor images of the most important portions of the structures, such as beneath salt. Conventional imaging methods do not properly correct for the conversions and bending that seismic waves can undergo while traveling through these complex structures. Some structures produce mode conversions (elastic wave effects) which result in misleading artifacts in the images. In other cases, strong geological discontinuities will bend and distort seismic waves and may cause severe multipathing. In the most complex cases both elastic and multipathing effects combine to make accurate imaging extremely difficult. Although if they are not properly imaged they can produce artifacts, elastic waves can also provide valuable information. To better exploit that information, industry is increasingly collecting multi-component seismic data. Multi-component data can provide much better imaging than single-component data in some situations (such as shallow gas columns), and can also provide rock parameter information that is essential for accurate reservoir modeling. However, processing and interpreting multi-component data increases the already heavy computational burden of imaging of conventional 3-D seismic data, and requires much better understanding of elastic wave propagation than we now have.

To help industry overcome these challenges and better exploit the opportunities provided by these new data, a collaborative industry-national laboratory-university project is carrying out research efforts aimed at increased understanding of 3-D wave propagation effects in complex geological structures. This project is titled "Next-Generation Seismic Modeling and Imaging". The U.S. Department of Energy, through the National Gas and Oil Technology Partnership of the Office of Fossil Energy, provides funding for the national laboratory and university participants. Industry participants are self-funded, and many also provide in-kind contributions to the project. The goals of this work are: 1) to obtain more accurate and realistic 3-D seismic wave modeling methods and synthetic seismic data, and 2) to develop and test new, more reliable 3-D imaging methods. The project includes two tasks, each of which focuses on one of the two goals.

The first task of the project is devoted to developing and applying numerical (forward) modeling methods. Forward modeling of seismic data from complicated structures has provided new insights and the impetus to develop new methods of imaging to solve problems with existing methods. An acoustic data set produced by the SEG/EAGE numerical modeling project (see "Joint project aims to facilitate, expand, use of numerical data", by L. House and F. Aminzadeh, The American Oil and Gas Reporter, Feb 1996, (v 39, # 2) p. 78-85 , and "Joint Initiative Produces 3-D Models", by F. Aminzadeh and N. Burkhard, The American Oil and Gas Reporter, Feb 1995 (v 38, #2), p 63-69) is now widely used by researchers in both industry and academia. A key strength of this data set is its broad availability, which has led to a shared understanding of the imaging results that have been derived from it. The data set was generated by calculations that employed acoustic only wave calculations because at that time, elastic wave calculations were impractical. Advances in computing that have occurred since then have made elastic wave modeling more feasible. This work will build upon the success of a previous DOE-sponsored project, "Testing Advanced Computational Tools for 3D Seismic Analysis Using the SEG/EAGE Model Dataset".

High quality elastic numerical data provides challenging tests of 3-D imaging methods and rigorous tests of current seismic attribute methodology. The 3-D elastic numerical modeling task will focus on a few modeling problems in which elastic wave effects are significant. The project’s industry participants will define and build the models that will be used, and portions of them will be selected for computing 3-D elastic numerical data. The computations will be done primarily at the two national laboratories that are participating in the project: Los Alamos (LANL) and Lawrence Livermore (LLNL). The calculations will be done with the elastic modeling code E3D. E3D is being used for a number of acoustic and elastic modeling problems, including seismic exploration, earthquake hazards, nuclear nonproliferation, and biotechnology. It has been provided to several industry participants and research organizations. E3D can operate in a several modes, including 2-D, 3-D, acoustic, and elastic. The code is computationally efficient and portable across many computing platforms, ranging from pc-clusters to massively parallel supercomputers. E3D has been used to create elastic data that represent a subset of the larger acoustic data set computed from the SEG/EAGE model. Although calculating elastic model data is the primary objective of this task, we also plan to investigate the effects of attenuation, topography, and anisotropy and add these capabilities to E3D if warranted.

The choice and design of the models and model parameters will be made in collaboration with project participants. The project seeks to complement the modeling efforts being done by participants, and to concentrate on the problems and issues that are of greatest common interest. In addition, this task will use the calculated data to calibrate and validate current seismic attribute technology, including coherence, dip/azimuth, spectral decomposition, impedance inversion, and AVO.

The goal of the second task of the project is to make wave-equation methods efficient enough that they can be the preferred tools for imaging in complex areas. Effort are focused on the following three specific topics: 1) improving the accuracy and computational efficiency of common-azimuth migration; 2) refining techniques for extracting AVA information from common-azimuth migration and its derivatives; and 3) developing a practical methodology for performing wave-equation migration velocity analysis (WEMVA).

The accuracy and efficiency of common-azimuth migration will be improved in two ways. First, the equations for common-azimuth migration will be generalized to expand their range of applicability to narrow-azimuth migration. Second, applying a recently developed theory for wide-angle space-wavenumber downward-continuation will increase the accuracy of the numerical solutions for the common-azimuth and narrow-azimuth migration equations. Also, the amplitude behavior of one-way downward continuation operators in heterogeneous media will be studied to improve handling of trace amplitudes. We also developed a new method that iteratively maximizes the quality of the migrated image obtained by downward-continuation migration. The method has been tested with 2-D synthetic examples, but it needs further theoretical and methodological developments to become a practical tool.

Results from the project are made available as widely as possible to all participants, although some input data sets and computational tools are considered proprietary. Industry participants are self-nominating, and are welcome to join at any time. There are no formal arrangements or agreements needed.

This effort is a collaboration between SEG (through a subcommittee of the SEG Research Committee) and the U.S. Department of Energy (through the National Gas and Oil Technology Partnership) and national laboratories and universities. The U.S. Department of Energy provides funding for the national laboratory participants, and much of the funding for the university participants. The industry participants fund their own time, and provide in-kind contributions to the project.

As industry searches for new oil and gas sources in ever more complex geologic structures, accurate and reliable seismic imaging is increasingly important. These complex geological structures can be very difficult to image properly, and conventional 3-D imaging methods often provide poor images of the most important portions of the structures, such as beneath salt. Conventional imaging methods do not properly correct for the conversions and bending that seismic waves can undergo while traveling through these complex structures. Some structures produce mode conversions (elastic wave effects) which result in misleading artifacts in the images. In other cases, strong geological discontinuities will bend and distort seismic waves and may cause severe multipathing. In the most complex cases both elastic and multipathing effects combine to make accurate imaging extremely difficult. Although if they are not properly imaged they can produce artifacts, elastic waves can also provide valuable information. To better exploit that information, industry is increasingly collecting multi-component seismic data. Multi-component data can provide much better imaging than single-component data in some situations (such as shallow gas columns), and can also provide rock parameter information that is essential for accurate reservoir modeling. However, processing and interpreting multi-component data increases the already heavy computational burden of imaging of conventional 3-D seismic data, and requires much better understanding of elastic wave propagation than we now have.

To help industry overcome these challenges and better exploit the opportunities provided by these new data, a collaborative industry-national laboratory-university project is carrying out research efforts aimed at increased understanding of 3-D wave propagation effects in complex geological structures. This project is titled "Next-Generation Seismic Modeling and Imaging". The U.S. Department of Energy, through the National Gas and Oil Technology Partnership of the Office of Fossil Energy, provides funding for the national laboratory and university participants. Industry participants are self-funded, and many also provide in-kind contributions to the project. The goals of this work are: 1) to obtain more accurate and realistic 3-D seismic wave modeling methods and synthetic seismic data, and 2) to develop and test new, more reliable 3-D imaging methods. The project includes two tasks, each of which focuses on one of the two goals.

The first task of the project is devoted to developing and applying numerical (forward) modeling methods. Forward modeling of seismic data from complicated structures has provided new insights and the impetus to develop new methods of imaging to solve problems with existing methods. An acoustic data set produced by the SEG/EAGE numerical modeling project (see "Joint project aims to facilitate, expand, use of numerical data", by L. House and F. Aminzadeh, The American Oil and Gas Reporter, Feb 1996, (v 39, # 2) p. 78-85 , and "Joint Initiative Produces 3-D Models", by F. Aminzadeh and N. Burkhard, The American Oil and Gas Reporter, Feb 1995 (v 38, #2), p 63-69) is now widely used by researchers in both industry and academia. A key strength of this data set is its broad availability, which has led to a shared understanding of the imaging results that have been derived from it. The data set was generated by calculations that employed acoustic only wave calculations because at that time, elastic wave calculations were impractical. Advances in computing that have occurred since then have made elastic wave modeling more feasible. This work will build upon the success of a previous DOE-sponsored project, "Testing Advanced Computational Tools for 3D Seismic Analysis Using the SEG/EAGE Model Dataset".

High quality elastic numerical data provides challenging tests of 3-D imaging methods and rigorous tests of current seismic attribute methodology. The 3-D elastic numerical modeling task will focus on a few modeling problems in which elastic wave effects are significant. The project’s industry participants will define and build the models that will be used, and portions of them will be selected for computing 3-D elastic numerical data. The computations will be done primarily at the two national laboratories that are participating in the project: Los Alamos (LANL) and Lawrence Livermore (LLNL). The calculations will be done with the elastic modeling code E3D. E3D is being used for a number of acoustic and elastic modeling problems, including seismic exploration, earthquake hazards, nuclear nonproliferation, and biotechnology. It has been provided to several industry participants and research organizations. E3D can operate in a several modes, including 2-D, 3-D, acoustic, and elastic. The code is computationally efficient and portable across many computing platforms, ranging from pc-clusters to massively parallel supercomputers. E3D has been used to create elastic data that represent a subset of the larger acoustic data set computed from the SEG/EAGE model. Although calculating elastic model data is the primary objective of this task, we also plan to investigate the effects of attenuation, topography, and anisotropy and add these capabilities to E3D if warranted.

The choice and design of the models and model parameters will be made in collaboration with project participants. The project seeks to complement the modeling efforts being done by participants, and to concentrate on the problems and issues that are of greatest common interest. In addition, this task will use the calculated data to calibrate and validate current seismic attribute technology, including coherence, dip/azimuth, spectral decomposition, impedance inversion, and AVO.

The goal of the second task of the project is to make wave-equation methods efficient enough that they can be the preferred tools for imaging in complex areas. Effort are focused on the following three specific topics: 1) improving the accuracy and computational efficiency of common-azimuth migration; 2) refining techniques for extracting AVA information from common-azimuth migration and its derivatives; and 3) developing a practical methodology for performing wave-equation migration velocity analysis (WEMVA).

The accuracy and efficiency of common-azimuth migration will be improved in two ways. First, the equations for common-azimuth migration will be generalized to expand their range of applicability to narrow-azimuth migration. Second, applying a recently developed theory for wide-angle space-wavenumber downward-continuation will increase the accuracy of the numerical solutions for the common-azimuth and narrow-azimuth migration equations. Also, the amplitude behavior of one-way downward continuation operators in heterogeneous media will be studied to improve handling of trace amplitudes. We also developed a new method that iteratively maximizes the quality of the migrated image obtained by downward-continuation migration. The method has been tested with 2-D synthetic examples, but it needs further theoretical and methodological developments to become a practical tool.

Results from the project are made available as widely as possible to all participants, although some input data sets and computational tools are considered proprietary. Industry participants are self-nominating, and are welcome to join at any time. There are no formal arrangements or agreements needed.

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