Basic Concepts In 3-D Surveys
There are some new aspects to the survey design in three dimensions relative to 2-D surveys. The 2-D surveys are as linear as the terrain allows. Source and receiver are normally in-line with each other. Arrays may be multidimensional, but most often are also in the line of the survey. For 3-D surveys, this is seldom the case.
The source interval of a 2-D survey must be extended to include a definition of the source line. When the sources are in-line, the source line overlays the receiver line, so only the source interval needs to be determined. This is not the case for 3-D surveys, and a source line must be defined. In the most used designs, the source line is now orthogonal to the receiver lines, as in Figure 65.
Note that the receiver line becomes the receiver lines. As many receiver lines are laid out as the equipment for acquisition allows. Also, the receiver layout may not be lines but circles, checkerboards, and other patterns developed for 3-D surveys. Thus the simple parameters that defined the traditional 2-D line now must be extended to include much more geometry, more than you may be able to do on the back of an envelope, as was the case for 2-D lines.
The 3-D survey also includes multiple source lines as well as multiple receiver lines, and it is possible to record two source lines simultaneously using vibration techniques. The arrays also may respond in a less predictable manner as they
Figures & Tables
Designing Seismic Surveys in Two and Three Dimensions
“Written for both the nongeophysicist and the practicing geophysicist, this book collects many of the formulas, principles, concepts, and field approximations of seismic survey design. The basics of 2D and 3D design in this book offer an introduction to the nongeophysicist and provide a good review for the practicing geophysicist. Arrays, obstacles, and special problems are discussed, as are aspects introduced by 3D surveys. The author explores design attributes such as fold, costs, and field time.”