3-D wave-equation prestack imaging under salt

For the SEG-EAGE salt data set, common-azimuth migration produces better images in the subsalt than single-arrival Kirchhoff migration, at a similar computational cost. Subsalt reflectors are better imaged and the typical Kirchhoff artifacts caused by severe multipathing disappear. We show how angle-domain Common Image Gathers (CIG) can be easily extracted from prestack wavefield downward continued using wave-equation methods. These CIG gathers can be used to estimate the velocity function and analyze reflection amplitude as a function of aperture angle (AVA). A complete wave-equation imaging procedure that includes: migration, migrationvelocityanalysis, andAVA analysis, can thus be applied to study reservoirs below complex overburden. This procedure should be more accurate and reliable than conventional Kirchhoff procedures when severe multipathing affects reflections.