3D Data Geometries
Because of practical and economical considerations, 3D surveys are not acquired with complete and regular sampling of the spatial axes. The design of 3D surveys presents many more degrees of freedom than does the design of 2D surveys, and it has no standard or unique solution. Design of 3D acquisition geometries is the result of many trade-offs among data quality, logistics, and cost. Furthermore, nominal designs commonly must be modified to accommodate operational obstacles encountered in the field.
Data-acquisition design and processing are becoming ever more connected, because characteristics of the acquisition geometry strongly influence the data processing. One must understand the principles of acquisition design if one is to understand many dataprocessing issues.
The main goal of conventional acquisition design is to obtain an adequately and regularly sampled stacked cube that can be imaged accurately by poststack migration. Other important parameters are the minimum and maximum offsets. Minimum offset must be small enough to guarantee adequate coverage of shallow targets. Maximum offset must be large enough to allow accurate velocity estimates, which are necessary for both stacking and poststack imaging. However, in common acquisition geometries, sampling of the offset axes may be inadequate when the data require prestack processing that is more sophisticated prestack processing than simple stacking. Even application of standard dip moveout (DMO) (Chapter 4) may be problematic with some commonly used acquisition geometries. In such cases, the requirement that midpoint axes be adequately sampled is not sufficient, because offset and azimuth sampling also are