US 7,095,678 B2Granted

Method for seismic imaging in geologically complex formations

AssigneeExxonMobil Upstream Research Company

InventorsGraham A. Winbow, Thomas Edward Clee

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Abstract

A method for multipath imaging of three-dimensional volumes of seismic data, given the subsurface velocity distribution. Ray tracing is used to generate the volumes of information needed for migration, but using coarse-scaled grids for computational efficiency. Interpolation methods are disclosed that address the specific shot points and receiver locations and that enable a final image on a grid with the desired resolution. Data storage and retrieval techniques are also disclosed.

Claims25

Dependent claims

A computer-based method for controlled amplitude imaging of a target geologic formation in a subsurface region using a three-dimensional seismic data volume acquired from the subsurface region and a known velocity distribution for the subsurface region, said seismic data comprising a plurality of seismic traces, each trace having a known shot point location and a known receiver location, said method comprising the steps of:

(a) discretizing into a grid of cells a three-dimensional subsurface space containing the target formation, each such image cell containing a plurality of points of a pre-selected three-dimensional image point grid, cell dimensions being chosen to balance data storage requirements with imaging accuracy;
(b) discretizing into a grid of cells the surface above the target formation, the dimensions of such surface cells being chosen relative to shot point and receiver spacings so as to balance data storage requirements with imaging accuracy;
(c) computing ray map files from the velocity distribution information, said files representing all physically significant ray paths connecting a representative point in a surface cell to a representative point in an image cell, using a velocity distribution for the subsurface region to determine the ray paths, said ray map files containing at least the surface cell to image cell travel time, the takeoff direction at each surface cell and the arrival direction at each image cell, said directions being specified in three-dimensional space;
(d) repeating step (c) for each surface cell and each image cell;
(e) storing the ray map files in computer memory;
(f) interpolating travel times from the ray map files, said interpolated times being times from the particular shot point and receiver locations associated with one seismic data trace down to each point on the image point grid for each said physically significant ray path connecting same, said interpolation comprising:
interpolating a surface cell representative point near each said particular shot point location and each said particular receiver point location;
and interpolating an image cell representative point near said each point on the image grid;
wherein said interpolations are implemented using the ray direction information in the corresponding ray map file in order to ensure that interpolation is made between points on the same branch of the travel time surface;
(g) repeating step (f) for each trace in the seismic data volume;
and
(h) migrating the seismic data using the interpolated travel times and the ray amplitudes.

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Dependencies are inferred from the claim text.

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Abstract

(a) discretizing into a grid of cells a three-dimensional subsurface space containing the target formation, each such image cell containing a plurality of points of a pre-selected three-dimensional image point grid, cell dimensions being chosen to balance data storage requirements with imaging accuracy;
(b) discretizing into a grid of cells the surface above the target formation, the dimensions of such surface cells being chosen relative to shot point and receiver spacings so as to balance data storage requirements with imaging accuracy;
(c) computing ray map files from the velocity distribution information, said files representing all physically significant ray paths connecting a representative point in a surface cell to a representative point in an image cell, using a velocity distribution for the subsurface region to determine the ray paths, said ray map files containing at least the surface cell to image cell travel time, the takeoff direction at each surface cell and the arrival direction at each image cell, said directions being specified in three-dimensional space;
(d) repeating step (c) for each surface cell and each image cell;
(e) storing the ray map files in computer memory;
(f) interpolating travel times from the ray map files, said interpolated times being times from the particular shot point and receiver locations associated with one seismic data trace down to each point on the image point grid for each said physically significant ray path connecting same, said interpolation comprising:
interpolating a surface cell representative point near each said particular shot point location and each said particular receiver point location;
and interpolating an image cell representative point near said each point on the image grid;
wherein said interpolations are implemented using the ray direction information in the corresponding ray map file in order to ensure that interpolation is made between points on the same branch of the travel time surface;
(g) repeating step (f) for each trace in the seismic data volume;
and
(h) migrating the seismic data using the interpolated travel times and the ray amplitudes.

9 more elements