Narrow- versus wide-azimuth land 3D seismic surveys

Abstract

It appears that there are two very distinct schools of thought with respect to the patch configuration for land 3D seismic surveys; often the like or dislike of one over another is based on which part of the business one is involved in rather than any scientific reason. Oil and gas companies (after all the clients) may prefer a wide recording patch to maximize the truly 3D coverage while acquisition contractors (if given a choice) may opt for a narrow recording patch for operational reasons. There are more reasons than these to consider either recording patch and the benefits of both need to be considered when designing a 3D survey. The distinction between narrow- and wide-azimuth surveys is made on the basis of the aspect ratio of the recording patch. The aspect ratio is defined as the cross-line dimension of the patch divided by the in-line dimension. Recording patches with an aspect ratio of less than 0.5 are narrow azimuth and those greater than 0.5 are wide azimuth (Cordsen et al., 2000). Wide-azimuth patches often have aspect ratios of 0.8-1.0 (Figure 1a); narrow-azimuth patches may very well have aspect ratios as low as 0.2 (Figure 1b). Figure 1. Wide versus narrow patch—template and fold. In all figures showing lines, the receiver lines are laid out east-west and blue. Source lines are red. (a) Wide-azimuth template. (b) Narrow-azimuth template. (c) Wide-azimuth fold distribution at full offsets. (d) Narrow-azimuth fold distribution at full offsets. (e) Wide-azimuth fold distribution at 1500-m offsets. (f) Narrow-azimuth fold distribution at 1500-m offsets. Comparisons have been compiled to illustrate the major differences between narrow- and wide-azimuth acquisition using an orthogonal layout. Figures 1–3 compare a wide-azimuth acquisition consisting of a patch of 12 lines with 60 stations per line in the top row (a, c, e) to a …