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Abstract

The goal of seismic data acquisition and processing is to provide a realistic image of the subsurface structure of the Earth. Since that structure is three-dimensional, one might suspect that 2-D data acquisition and processing can be inadequate. That is indeed the case: 2-D seismic data can provide a misleading image of the earth’s subsurface, even for the simplest 3-D structures. Figure 161, for example, shows a reflector that has a dip direction perpendicular to the shooting direction of a 2-D seismic line. When the data are processed, the cross dip causes two problems in the image. First, the part of the reflector being imaged is not the part that actually lies vertically under the 2-D line, as an interpreter unaware of the cross dip would assume. Second, the reflector’s depth is incorrect. Both of these problems occur because the actual reflection points do not lie in the vertical plane below the line.

The solution to these problems is to record 3-D seismic data and to process them using 3-D rather than 2-D imaging algorithms. In 3-D acquisition, the data are collected over a 2-D surface area instead of along 1-D lines. After 3-D processing, reflection events appear as 2-D surfaces rather than as 1-D events. A dipping, reflecting plane such as that in Figure 161 is then correctly imaged.

French (1974) illustrated the benefits of 3-D versus 2-D seismic methods in a classical modeling study performed at Gulf Research Laboratories. One of French’s models (unpublished) had a normal fault

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