Method of measuring local similarities between several cubes containing seismic traces

摘要

A combination of seismic traces is extracted from each cube centered on a point. ACPG analysis is applied to form synthetic variables and a coherence value is then determined associated with the center point. This is repeated for each point common to the different cubes and the combined coherence values are regrouped to form a coherence cube interpreting the similarities : The process involves: (a) extracting a volume location centered on the same running point and composed of a combination of a limited number of seismic traces (b) applying Analysis in Generalized Main Components (ACPG) analysis technique to the extracted groups of seismic attributes to form synthetic variables, (c) determining a coherence value from the synthetic variables which is allotted to the running point, (d) repeating stages (a) to (c) for each point common to the different cubes and (e) regrouping the combined coherence values to form a cube of coherence interpreting the similarities. For each point, the coherence value is the mean square value of the correlations between a limited number k of synthetic variables and their projections on the cubes in the area of the running point. The value of k synthetic variables is determined as the smallest number of synthetic variables to reach a preset variance threshold explained by projections of the synthetic variables on each cube., or according to the correlations of the synthetic variables with groups of attributes associated with the volume around the running point, the coherence value at the point being equal to the weighted sum of the squares of correlations of the synthetic variables and their projections on the cubes around the running point. For a defined correlation value, the weighting is chosen as the percentage variation explained by projection of the synthetic variable on the corresponding group divided by the sum of the variances of all the projections of synthetic variables considered on the same group. A threshold is fixed on the percentage variance explained by projection of the synthetic variables around the running point which are considered, the coherence value is therefore equal to the weighted sum of the squares of the correlations between the synthetic variables and their projections on the cubes around the running point such that the number of synthetic variables taken into consideration allows the threshold to be reached. The weighting is p times the fixed variance threshold where p is the number of seismic cubes considered. A volume around the seismic trace cubes is extracted each corresponding to the same angle of incidence or the same displacement or offset, or successive explorations of the area. A volume around the cubes is extracted from the residues obtained from a stratigraphic inversion before or after summation.