3D symmetric sampling of sparse acquisition geometries

Abstract

3D symmetric sampling introduced in the 1990s is characterized by dense sampling of two of the four spatial coordinates. The two sparsely sampled coordinates determine the periodicity of the geometry and the dimension of the offset-vector tiles that can be used to generate pseudocommon-offset-vector gathers. These gathers turn out to be useful for prestack processing applications, such as regularization, migration velocity analysis, and azimuthal anisotropy analysis. Although single-point acquisition is the ideal acquisition method, it is not necessarily better than array-based acquisition. Field arrays are still useful in suppressing noise and need not harm signal in most practical cases. In hybrid geometries three spatial coordinates are sampled densely. In all published cases at least two of the three are sampled quite coarsely and may not provide the best quality for the given trace density. Coil geometry (sailing in circles) is a special case of wide-azimuth towed streamer acquisition. It is essentially a random geometry that should be modifiable into a geometry with regularly sampled midpoints, absolute offsets and azimuths. Despite recent technological developments, the basic idea of 3D symmetric sampling still is a highly useful principle for the design of land and marine 3D seismic surveys.