Imaging with Downgoing and Upgoing Wavefield - 2D Prestack Mirror and Reciprocal Shot Migration

Abstract

The traditional geometry for nodes acquisition is a sparse receiver spacing and dense shooting. However, in the presence of salt sediments this geometry can lead to poor illumination. An efficient solution for this problem is the use of downgoing waves which enables a wider coverage of the subsurface. This paper presents an application of the mirror migration method, which uses the downgoing wavefield (ghost reflections), in conjunction with the reciprocal shot migration technique (upgoing wavefield) to better illuminate structures below salt sediments. In order to increase the illumination, both migration results are summed and analyzed. It is also evaluated the influence of increasing the receiver spacing. The migration results using downgoing wavefield and the summation of both techniques (reciprocal and mirrored migration) generated better images of deep reflectors than using only the upgoing wavefield (conventionally, the only wavefield used). This work aims to provide a better understanding of the advantages in combining both techniques (upgoing and downgoing) with wave equation migration methods.