NORTH-SEA RESERVOIR DESCRIPTION - BENEFITS OF AN ELASTIC MIGRATION INVERSION APPLIED TO MULTICOMPONENT VERTICAL SEISMIC PROFILE DATA

A linearized elastic migration/inversion (M/I) technique is applied to multicomponent offset VSP data collected in the North Sea. High-resolution elastic images of the target zone (P- and S-wave velocities and density) are obtained from upgoing P-P and P-S wave fields. These M/I images are an approximate representation of rapid variations of subsurface parameters. Three image confidence criteria provide a measure of uncertainty in the interpretation. VSP-CDP transform maps assisted in the definition of the confidence region in M/I images. M/I was helpful in delineating the Brent reservoir, and detecting a two-fault system. Preliminary interpretation indicates an increase in Poisson's ratio at the top of the reservoir. Surface data were not able to image this target due to strong multiples at the Cretaceous base. This is the first time elastic depth images have been obtained from M/I of offset VSP field data. -from Authors