STUDIES OF MULTICOMPONENT SEISMIC POLARITY AND AMPLITUDE

Alexandru Vant

ABSTRACT

Assuming the SEG (Society of Exploration Geophysics) polarity standard is followed, there are some cases in which reflections on the compressional (P-P) and converted-wave (P-S) sections show opposite polarities. This situation makes the correlation and interpretation processes more difficult.

To find conditions that relate polarity to elastic parameters, I derived a new approximation for the P-S reflection coefficient (RPS) and also modelled seismic responses from a wide range of geologically plausible interfaces using acoustic P- and S-wave velocities and densities. In also investigate the polarity consistency with offset and how missing velocity or density well-logs used to create synthetic shot-gathers and stacks affect the interpretation process.

As a side result, I show that, with small changes, the new RPS approximation is suitable for AVO (amplitude variation with offset) studies and also describe a more accurate way of computing the theoretical AVO attributes.

Opposite polarities on P-P and P-S sections were found to be associated with situations where not all the rock parameters change in the same direction (e.g. velocities increase and density decreases) across the interface.

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