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.

Seismic imaging across fault systems in the Abitibi greenstone belt – An analysis of pre- and post-stack migration approaches in the Chibougamau area, Quebec, Canada

“…The crooked nature of the surveys encouraged performing CDMO analysis to take into account the effect of out -of-plane structures. For a 3D survey, equal azimuthal distribution, typically contributed by inline and crossline components, satisfies the symmetric sampling (Vermeer 1990(Vermeer , 1998(Vermeer , 2010. In the case of a 2D survey, reciprocity of shot/receiver gathers suggest that properties of the continuous wavefield in a common shot/VP gather are the same as the properties of a common receiver gather.…”

“…Sampling requirements are the same for both domains and results in symmetric sampling. The immediate requirement of the 2D symmetric sampling is that the continuous wave field should be alias-free for ground-roll and low velocity noise (Vermeer, 2010). To satisfy an alias-free, continuous wavefield sampling, the basic sampling interval (∆ ) is defined as Eq.…”

“…To satisfy an alias-free, continuous wavefield sampling, the basic sampling interval (∆ ) is defined as Eq. (A1) (Vermeer, 2010):…”

3D Seismic Survey Design, Second edition

“…The two spatial coordinates that are fixed in each 3D subset determine the sparsity of the 3D acquisition geometry (Vermeer, 2010). These intervals represent the minimum distance of the centers of the 3D subsets from each other.…”

“…The limitations of parallel geometry have led to many discussions and experiments that confirm the benefit of long offsets for all shot-receiver azimuths; examples are discussed in Section 5.3.14 on multiazimuth acquisition. Next to the preference for long offsets for all azimuths, 3D symmetric sampling aims for proper sampling of two spatial coordinates; the coarsely sampled coordinates determine the sparsity of the geometry (Vermeer, 2010).…”