Abstract: 3D preSDM model building via CRP image gather scans: a North Sea case study

JONES, IAN F., MARTIN GRIMSHAW, KEITH IBBOTSON, Compagnie Generale de Geophysique, UK, and BRENT JOLLEY

Prior to performing a full-volume 3D pre-stack depth migration (preSDM) it is necessary to be confident that the travel times are being computed through a reliable velocity-depth model. It is the derivation of such a reliable model that we concern ourselves with in this work, via the use of a new velocity update scheme.

We commence by using 3D tomographic inversion to obtain a close starting model. Thereafter we proceed to update the velocity field for a given layer using the new technique, and then specify the layer geometry for the horizon in question using 3D post-stack depth migration. This procedure is repeated as required for all layers of the velocity-depth model). In essence this processing flow comprises an inner loop for the interval velocity update (using 3D preSDM), and an outer loop for the layer geometry update (using postSDM).

The core of the new velocity updating tool relies on taking the travel-time table associated with the 3D preSDM, and making several renditions of it. Each rendition of the travel-time table is then perturbed so as to span a desired range of velocities. A unique 3D preSDM is computed for each rendition of the table, so as to output image gathers on a suitable grid. Velocity information can thereby be assessed, forming the basis of the new update scheme.

Results for a North Sea case study are shown.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria