Seismic velocity analysis for class II sands
AssigneePhillips Petroleum Company
InventorsDennis B. Neff, Carl B. Sigler, III
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Abstract
A method and apparatus are disclosed for processing seismic trace data to distinguish Class II sand formations sandwiched between low and high porosity layers, where the intermediate sand layer causes a polarity reversal with offset in seismic reflections. A velocity analysis of data from a vertical seismic section is generated to include coherency contours corresponding to polarity reversals in the seismic traces by using an extended crosscorrelation algorithm for multi-trace coherency. The velocity analysis thus indicates a stacking velocity that will maximize coherency of the seismic traces exhibiting the polarity reversal.
Claims12
A method of processing seismic data for a velocity analysis, wherein said data corresponds to a vertical seismic record section, and wherein trace data in said record section includes multiple offsets, and further includes traces exhibiting a polarity reversal with offset in at least a portion of said record section, and wherein said traces exhibiting polarity reversal are presented as contours of coherency in a graphic display of said velocity analysis, said method comprising:
- a) applying normal moveout (NMO) to all traces in said seismic record section;
- b) defining a plurality of subgroups, wherein each subgroup comprises a plurality of adjacent traces in said record section, and further defining a length of a time for a comparison window;
- c) determining a measure of multi-trace coherency for each of said plurality of subgroups using a sliding time window technique and an extended cross-correlation algorithm for determining said measure of multi-trace coherency, and wherein said measure of multi-trace coherency includes values which are representative of said traces exhibiting polarity reversal with offset;
- and
- d) graphically displaying said velocity analysis in a time-velocity domain, and including contours of said multi-trace coherency based on said measure of multi-trace coherency for each of said plurality of subgroups determined in step c).
A method of analyzing seismic survey traces to distinguish the presence of sand formations in a region of the earth corresponding to said seismic survey, wherein said seismic traces are arranged in a vertical seismic record section, and wherein trace data in said record section includes multiple offsets, and further includes traces exhibiting a polarity reversal with offset in at least a portion of said record section, and further wherein said traces exhibiting polarity reversal are presented as contours of coherency in a graphic display of said velocity analysis, said method comprising:
- a) applying normal moveout (NMO) to all traces in said seismic survey;
- b) defining a plurality of subgroups, wherein each subgroup comprises a plurality of adjacent traces in said record section, and further defining a length of a time for a comparison window;
- c) determining a measure of multi-trace coherency for each of said plurality of subgroups using a sliding time window technique and an extended cross-correlation algorithm for determining said measure of multi-trace coherency, and wherein said measure of multi-trace coherency includes values which are representative of said traces exhibiting a polarity reversal with offset;
- d) graphically displaying said velocity analysis in a time-velocity domain, and including contours of said multi-trace coherency based on said measure of multi-trace coherency for each of said plurality of subgroups determined in step c);
- and
- e) using said velocity analysis for determining a stacking velocity that will maximize coherency of said traces exhibiting a polarity reversal with offset to distinguish the presence of sand formations.
Apparatus for analyzing seismic survey traces to distinguish the presence of sand formations in a region of the earth corresponding to said seismic survey, wherein said seismic traces are arranged in a vertical seismic record section, and wherein trace data in said record section includes multiple offsets, and further includes traces exhibiting a polarity reversal with offset in at least a portion of said record section, and firer wherein said traces exhibiting polarity reversal are presented as contours of coherency in a graphic display of said velocity analysis, said apparatus comprising:
- a computer programmed for:
- i) applying normal moveout (NMO) to all traces in said seismic survey;
- ii) defining a plurality of subgroups, wherein each subgroup comprises a plurality of adjacent traces in said record section, and further defining a length of a time for a comparison window;
- iii) determining a measure of multi-trace coherency for each of said plurality of subgroups using a sliding time window technique and an extended cross-correlation algorithm for determining said measure of multi-trace coherency, and wherein said measure of multi-trace coherency includes values which are representative of said traces exhibiting a polarity reversal with offset;
- iv) graphically displaying said velocity analysis in a time-velocity domain, and including contours of said multi-trace coherency based on said measure of multi-trace coherency for each of said plurality of subgroups determined in step c);
- and
- v) using said velocity analysis for determining a stacking velocity that will maximize coherency of said traces exhibiting a polarity reversal with offset to distinguish the presence of sand formations.
Dependencies are inferred from the claim text.