Introduction

In an ideal world, a 3-D seismic survey would have infinite extents and dense shot and receiver grids over the entire x-y plane. This would provide the best illumination possible everywhere in the subsurface. In our world, our limited source-receiver geometries allow energy to leave the survey and the density of our shot and receiver arrays depends on the equipment available. For 3-D surveys, the geometry leads to limited azimuth ranges dependent on the direction in which the survey is shot. The illumination itself depends on the subsurface structure. For all of these reasons, shooting our surveys in different directions will result in different subsurface illumination.

Some studies have been done comparing strike direction and dip direction surveys, which can be considered to be a special case of any two surveys shot in different directions over the same area. O'Connell et al. (1993) found that for many CMP-based processes, strike direction datasets had advantages over dip directions. Etgen and Regone (1998) showed that there are differences in multiple attenuation and illumination between strike and dip direction surveys.

In this paper, I will examine the results of common azimuth migration of 3-D datasets oriented along the dip and the strike directions of the Amoco 2.5-D Carpathian Mountains overthrusting the North Sea. I will explain how the differences in the images might be used to compensate for illumination problems and theorize that these problems may be overcome by using a regularized inversion of both datasets to produce images that combine the illumination of both.