Effect of Curvature on Seismic Data and Amplitude Analysis: A Modeling Study

Abstract

The effect of curvature upon AVO-analysis and the capability of Kirchhoff time migration to remove these effects were investigated in this thesis. Curvature focuses or de-focuses seismic waves depending on the shape of the structure. If not removed or accounted for, such effects could introduce false anomalies in the seismic data that could be misinterpreted. A prospect from the Norwegian Sea, situated in the basin of a graben system provided motivation for the work in this thesis. Analysis of synthetic data from simple geological models of synclines, together with a more realistic model, was done to investigate this. Standard pre-stack Kirchhoff migration was applied during processing before analysis was performed. Prismatic waves and refractions were observed distorting the migrated data and could potentially cause problems in AVO-analysis. Results predicted that false anomalies that can be misinterpreted as fluid effects could be introduced by the refracted/prismatic waves. The results did predict though, that strong curvature and large contrasts across interfaces were required to obtain such effects in the offset range commonly utilized in AVO-analysis. The problem was expected to be more relevant for analysis where larger offsets are used. Pre-stack Kirchhoff time migration incorrectly recovered reflection coefficients, but handled curvature effects sufficiently. Deviations from the analytical solutions were observed, but the estimated parameters followed a compaction/background trend in cross plots. No anomalous trends were introduced by focusing/de-focusing effects in the results seen in this thesis. The results of this thesis could be relevant for future exploration, where prospects from analogue graben areas are investigated.