f 3D Prestack Depth Migration - an Aid to Development Drilling

The 3D seismic survey discussed here was acquired in 1991 and covers an area of 300sq kms of the UK, Southern North Sea. Accurate time imaging is not possible due to structural complexities and lateral velocity contrasts in the section above the target horizon (Leman Sandstone). Structural complexities in the overburden are formed by salt walls and associated Mesozoic graben systems which juxtapose fast, dipping, Cretaceous, chalk against slow, Tertiary, clastic sediments. Conventional time processing, including DMO and migration does not yield a clear, accurately positioned image, and occasionally, no image is formed at the target horizon. Recent advances in computer hardware permat computationally intensive prestack depth migration to be performed on a 3D volume (a 7km x 11 km subset of the original dataset) which can produce more accurate images if an appropriate velocity/depth model is applied.