A 3-D Design Sequence
There are many ways to begin and complete a survey design. The specific sequence of steps that follow are general guidelines. Some design templates will dictate a different sequence or other parameters. The accent is on land surveys. Marine surveys have different constraints, obstacles, and freedoms, and are considered in Chapter 8.
The information gathering, modeling, and dimensionally independent parameters, such as offset range, are presumed to have been computed as previously described. The designer has determined the offset ranges, temporal frequency, required fold, bin size, and available field equipment capacity. Less direct variables such as survey size adjustments for migration and any azimuthal requirements are also presumed to be ready. Another assumption is that the 3-D design software can cope with the template you have in mind. A summary of the proposed sequence for developing a design script is:
Step 1.-Determine the subsurface bin size. Twice the chosen bin size is the source and receiver station spacings.
Step 2.-Compute the number of source stations per square kilometer required to achieve fold with the available equipment. The number of stations per square kilometer allows computation of the source line spacing.
Step 3.--Compute the receiver line spacing.
Step 4.--Find the number of receiver lines allowed by the field equipment constrained by the required offset ranges. The result is the template.
Step 5.--Decide on the x and y roll alongs.
Step 6.--Allow for obstacles and run analyses of the script for offset distribution in the bins, ranges
Figures & Tables
“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.”