Converted-mode angle-domain common-image gathers for migration velocity analysis

Daniel A. Rosales and Biondo Biondi

daniel@sep.stanford.edu, biondo@sep.stanford.edu

ABSTRACT

Common-image gathers are very useful for velocity and petrophysical analysis. Wavefield-extrapolation methods produce Angle-Domain Common-Image Gathers (ADCIGs). For the conventional PP case, ADCIGs are a function of the opening angle. The representation of ADCIGs for PS data (PS-ADCIGs) is more elaborate than for conventional ADCIGs. In PS-ADCIGs, the P-to-S velocity ratio is a major variable in transforming the subsurface offset to the opening angle, and in transforming this opening angle to either the P-incidence or the S-reflection angle. Numerical studies show that when the P-to-S velocity ratio and image midpoint information are not incorporated the error in computing PS-ADCIGs is enough to introduce artifacts in the velocity model.