--> ABSTRACT: Velocity-Depth Model Estimation for a Subsalt Target from the Southern Gas Basin of the North Sea, by Oz Yilmaz, Jeff Rutledge, Ottar Sandvin, and Bob Godfrey; #91019 (1996)
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Velocity-Previous HitDepthNext Hit Model Estimation for a Subsalt Target from the Southern Gas Basin of the North Sea

Oz Yilmaz, Jeff Rutledge, Ottar Sandvin, and Bob Godfrey

The Southern Gas Basin of the North Sea has been subjected to extensional tectonics, primarily in the east-west direction. Subsequent occurrence of the salt diapirism gave rise to the presence of complex structures. By doing a Previous HitdepthNext Hit-domain analysis of a Previous Hit3-DNext Hit seismic survey data from an area in the Southern Gas Basin, we delineated the structural geometry of the top Rotliegendes formation beneath the complex Zechstein diapiric formation. This required an accurate estimate of the velocity-Previous HitdepthNext Hit model above the Zechstein diapiric formation and removal of its deleterious effect on the underlying Permian sands of Rotliegendes and deeper targets. We conducted a layer-by-layer Previous HitdepthNext Hit. domain analysis, and used coherency inversion to estimate layer velocities and Previous Hit3-DNext Hit Previous HitpoststackNext Hit Previous HitdepthNext Hit Previous HitmigrationNext Hit to delineate reflector geometries down to top Zechstein. We ver fied the accuracy of the velocity-Previous HitdepthNext Hit model for the overburden above Zechstein by analyzing image gathers from prestack Previous HitdepthNext Hit Previous HitmigrationNext Hit. We then analyzed constant-half-space image-gather stacks to estimate velocities for the substratum including Zechstein and the underlying Carboniferous sequence. Finally, we performed Previous Hit3-DNext Hit prestack Previous HitdepthNext Hit Previous HitmigrationNext Hit to delineate the base Zechstein-top Rotliegendes geometry.

This study demonstrates the need for Previous HitdepthNext Hit-domain analysis of seismic data to derive accurate structure maps for targets beneath complex structures associated with salt and overthrust tectonics. The final output from Previous HitdepthNext Hit-domain analysis -- a velocity-Previous HitdepthTop model, can then be used as a canvas for a reservoir model.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California