Seismic velocity estimation from time migration
نویسندگان
چکیده
We address the problem of estimating seismic velocities inside the Earth which is necessary for obtaining seismic images in regular Cartesian coordinates. The main goals are to develop algorithms to convert time-migration velocities to true seismic velocities, and to convert time-migrated images to depth images in regular Cartesian coordinates. Our main results are three-fold. First, we establish a theoretical relation between the true seismic velocities and the ‘timemigration 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 ill posed, 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 timeto-depth conversion algorithms, based on Dijkstra-like 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 two-dimensional and three-dimensional problems, and we test them on a collection of both synthetic examples and field data.
منابع مشابه
Improved methods of reflection seismic data processing for velocity estimation, imaging, and interpretation
Seismic images and the geologic information they provide contribute significantly to our understanding of the earth’s subsurface. In this thesis, I focus on methods relevant for constructing and interpreting seismic images, including methods for velocity estimation, seismic imaging, and interpretation, which together address key aspects of reflection seismic data processing. Specifically, I pro...
متن کاملClosed-form expressions for map time-migration in VTI media and the applicability of map depth-migration in the presence of caustics
Provided the velocity of the medium is known and the the medium does not allow different reflectors to have identical surface seismic measurements that persist under small perturbations of the medium, map migration achieves a one-to-one mapping from surface seismic data to the subsurface seismic image by using the slopes in addition to the location (and time) of the events in the data. In this ...
متن کاملSeismic Velocity Estimation from Time Migration Velocities
We address the problem of estimating seismic velocities inside the earth which is necessary for obtaining seismic images in regular Cartesian coordinates. We derive a relation between the true seismic velocities and the routinely obtained so called ”time migration velocities”, which are some kind of mean velocities. We formulate an inverse problem and show that it is ill-posed. We suggest three...
متن کاملime-to-depth conversion and seismic velocity stimation using time-migration velocity
The objective was to build an efficient algorithm 1 to estimate seismic velocity from time-migration velocity, and 2 to convert time-migrated images to depth. We established theoretical relations between the time-migration velocity and seismic velocity in two and three dimensions using paraxial ray-tracing theory. The relation in two dimensions implies that the conventional Dix velocity is the ...
متن کاملSeismic data processing in vertically inhomogeneous Tl media
The first and most important step in processing data in transversely isotropic (TI) media for which velocities vary with depth is parameter estimation. The multilayer normal-moveout (NMO) equation for a dipping reflector provides the basis for extending the TI velocity analysis of Alkhalifah and Tsvankin to vertically inhomogeneous media. This NMO equation is based on a root-mean-square (rms) a...
متن کامل