Computer implemented method for improving a velocity model for seismic imaging
AssigneeRepsol ExploracióN, S.A
InventorsGermán LARRAZÁBAL, José OMANA
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Abstract
The present invention is in the field of seismic imaging of underground structures. The invention is a method for solving the uncertainty and instability generated in reservoir geometries due to salt bodies which causes the presence of artifacts in the velocity fields. The method is based in a desalting process and a further specific reconstruction of the sediments located in the domain of the image. Desalting means to remove salt volumes located within the domain wherein said process is followed by the replacement of good sediment velocity values and a careful iterative process avoiding the generation of artifacts.
Claims16
A computer implemented method for improving a velocity model for seismic imaging, said method comprising a migration module configured to migrate acoustic field data to correct a seismic image iteratively, the seismic image comprising voxels and/or pixels representing a velocity model of a region of a subsurface region, wherein said migration module at least returns a velocity correction (Δv) of the seismic image by carrying out a predetermined number of iterations;
- wherein the method comprises the steps:
- a) recording seismic waves at the earth's surface being acquired as acoustic field data,
- b) departing from an initial proposed image converting acoustic field data by the migration module, through a predetermined number of iterations, into an estimated seismic image comprising voxels and/or pixels representing the velocity model of the region of the subsurface region;
- c) identifying in the seismic image at least one salt region D1, at least one artifacts region D2, and at least one region D3 with no salt or artifacts;
- d) removing the voxels and/or pixels of the at least one salt region D1 and the at least one artifacts region D2 from the seismic image;
- e) filling the at least one salt region D1 and the at least one artifacts region D2 of the seismic image with voxels and/or pixels with velocity values interpolated from the velocity values of the at least one region D3 with no salt or artifacts;
- f) generating a velocity correction Δv for each voxel and/or pixel migrating the acoustic field data with the image obtained in step e) by means of the migration module carrying out a predetermined number of iterations n;
- g) updating the at least one salt region D1 and the at least one region D3 with no salt or artifacts with the velocity correction Δv for each voxel and/or pixel of said regions;
- h) updating the artifacts region D2 with a limited velocity correction Δv for each voxel and/or pixel of said regions, the limited velocity correction Δv being:
- or a bounded velocity correction;
- that is, the correction Δv if |Δv|≥Δmax being Δmax a positive predetermined bound or the correction sign (Δv)·Δmax if |Δv|≥Δmax being sing (Δv) the sign of Δv,
- or a damped velocity correction λΔv, being λ∈(0,1) a predetermined value.
- i) providing the seismic image corrected in the previous step.
Dependencies are inferred from the claim text.