Seismic velocity estimation from time migration
Abstract
This is concerned with imaging and wave propagation in nonhomogeneous media, and includes a collection of computational techniques, such as level set methods with material transport, Dijkstralike HamiltonJacobi solvers for first arrival Eikonal equations and techniques for data smoothing. The theoretical components include aspects of seismic ray theory, and the results rely on careful comparison with experiment and incorporation as input into large productionstyle geophysical processing codes. Producing an accurate image of the Earth's interior is a challenging aspect of oil recovery and earthquake analysis. The ultimate computational goal, which is to accurately produce a detailed interior map of the Earth's makeup on the basis of external soundings and measurements, is currently out of reach for several reasons. First, although vast amounts of data have been obtained in some regions, this has not been done uniformly, and the data contain noise and artifacts. Simply sifting through the data is a massive computational job. Second, the fundamental inverse problem, namely to deduce the local sound speeds of the earth that give rise to measured reacted signals, is exceedingly difficult: shadow zones and complex structures can make for illposed problems, and require vast computational resources. Nonetheless, seismic imaging is a crucial partmore »
 Authors:

 Univ. of California, Berkeley, CA (United States)
 Publication Date:
 Research Org.:
 Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
 Sponsoring Org.:
 USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC21)
 OSTI Identifier:
 923471
 Report Number(s):
 LBNL62726
R&D Project: 619701; BnR: KJ0101010; TRN: US200804%%1178
 DOE Contract Number:
 AC0205CH11231
 Resource Type:
 Thesis/Dissertation
 Country of Publication:
 United States
 Language:
 English
 Subject:
 99 GENERAL AND MISCELLANEOUS; ALGORITHMS; CARTESIAN COORDINATES; CONSTRUCTION; EARTHQUAKES; PROCESSING; SUBSURFACE STRUCTURES; TRANSPORT; VELOCITY; WAVE PROPAGATION
Citation Formats
Cameron, Maria Kourkina. Seismic velocity estimation from time migration. United States: N. p., 2007.
Web. doi:10.2172/923471.
Cameron, Maria Kourkina. Seismic velocity estimation from time migration. United States. doi:10.2172/923471.
Cameron, Maria Kourkina. Mon .
"Seismic velocity estimation from time migration". United States. doi:10.2172/923471. https://www.osti.gov/servlets/purl/923471.
@article{osti_923471,
title = {Seismic velocity estimation from time migration},
author = {Cameron, Maria Kourkina},
abstractNote = {This is concerned with imaging and wave propagation in nonhomogeneous media, and includes a collection of computational techniques, such as level set methods with material transport, Dijkstralike HamiltonJacobi solvers for first arrival Eikonal equations and techniques for data smoothing. The theoretical components include aspects of seismic ray theory, and the results rely on careful comparison with experiment and incorporation as input into large productionstyle geophysical processing codes. Producing an accurate image of the Earth's interior is a challenging aspect of oil recovery and earthquake analysis. The ultimate computational goal, which is to accurately produce a detailed interior map of the Earth's makeup on the basis of external soundings and measurements, is currently out of reach for several reasons. First, although vast amounts of data have been obtained in some regions, this has not been done uniformly, and the data contain noise and artifacts. Simply sifting through the data is a massive computational job. Second, the fundamental inverse problem, namely to deduce the local sound speeds of the earth that give rise to measured reacted signals, is exceedingly difficult: shadow zones and complex structures can make for illposed problems, and require vast computational resources. Nonetheless, seismic imaging is a crucial part of the oil and gas industry. Typically, one makes assumptions about the earth's substructure (such as laterally homogeneous layering), and then uses this model as input to an iterative procedure to build perturbations that more closely satisfy the measured data. Such models often break down when the material substructure is significantly complex: not surprisingly, this is often where the most interesting geological features lie. Data often come in a particular, somewhat nonphysical coordinate system, known as time migration coordinates. The construction of substructure models from these data is less and less reliable as the earth becomes horizontally nonconstant. Even mild lateral velocity variations can significantly distort subsurface structures on the time migrated images. Conversely, depth migration provides the potential for more accurate reconstructions, since it can handle significant lateral variations. However, this approach requires good input data, known as a 'velocity model'. We address the problem of estimating seismic velocities inside the earth, i.e., the problem of constructing a velocity model, which is necessary for obtaining seismic images in regular Cartesian coordinates. The main goals are to develop algorithms to convert timemigration velocities to true seismic velocities, and to convert timemigrated images to depth images in regular Cartesian coordinates. Our main results are threefold. First, we establish a theoretical relation between the true seismic velocities and the 'time migration velocities' using the paraxial ray tracing. Second, we formulate an appropriate inverse problem describing the relation between time migration velocities and depth velocities, and show that this problem is mathematically illposed, i.e., unstable to small perturbations. Third, we develop numerical algorithms to solve regularized versions of these equations which can be used to recover smoothed velocity variations. Our algorithms consist of efficient timetodepth conversion algorithms, based on Dijkstralike Fast Marching Methods, as well as level set and ray tracing algorithms for transforming Dix velocities into seismic velocities. Our algorithms are applied to both twodimensional and threedimensional problems, and we test them on a collection of both synthetic examples and field data.},
doi = {10.2172/923471},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2007},
month = {1}
}