Anisotropic pre‐stack time migration and pre‐stack depth migration for reservoir evaluation in offshore West Africa

Abstract

Summary An offshore West Africa seismic reservoir characterization study for an oil field appraisal using both pre-stack time and pre-stack depth migration data is presented. The known hydrocarbon seismic indicators of the region are first picked on the conventional pre-stack time migration (PSTM). But as the turbidite reservoirs are located on dipping layers (about 30°), the hydrocarbon indicators picked on time migration have to be laterally shifted to be correctly positioned in the final geological model. This is done through a map migration technique using a velocity model built with an approach involving 3D tomography and 3D Pre-Stack Depth Migration. The pre-stack depth migration (PSDM) is also implemented with the objective to tackle the geometrical uncertainties. Since this zone is located in a sand/shale environment, anisotropy is taken into account for an accurate depth conversion. This paper presents, in a first part, a combination of methods (from time to depth and from depth to time) which increases the confidence both in the time and in the depth interpretation for geological model building. In a second part, the PSDM work is extended for an attempt to use directly seismic attributes on depth migrated data in the angle domain. This approach is supposed to be more accurate than conventional approaches using time migration.