Inline / crossline templates
Learning objectives
- Compare orthogonal, brick, zigzag, and slanted templates on fold and azimuth
- Explain when a non-orthogonal template is worth the extra layout complexity
- Predict the near-offset signature of each template from geometry alone
- Choose a template given target requirements and logistics constraints
A template is the repeated geometry that defines how sources and receivers are laid out. Four standard templates cover 95% of land 3D:
- Orthogonal: shot lines perpendicular to receiver lines. Simple layout, uniform fold after edge taper, moderate azimuth spread. The default.
- Brick: orthogonal + alternate shot lines shifted by half a shot spacing in crossline. Smoother near-offset distribution; better for shallow targets.
- Zigzag: source drives a zigzag path along shot lines. Minimal crew moves, worse azimuth spread. Used in remote areas where logistics dominate.
- Slanted: shot lines at ~15° to receiver lines. Azimuth content steered into near-offsets. Niche.
How the choice is made
Orthogonal wins by default. Brick is worth the extra 10–15% layout cost when near-offset AVO matters (gas-sand or CO₂ targets) or when the shallow section is highly heterogeneous. Zigzag appears in desert or jungle work where a single crew drives a fixed path for weeks. Slanted is occasionally chosen when the target’s dominant dip direction needs extra near-offset azimuth coverage.
Marine templates are different
Marine streamer surveys don’t have this taxonomy — the vessel tows fixed sources and receivers in a single direction; the "template" is the vessel track pattern. WAZ (§4.7) adds side vessels; that’s the marine equivalent of going from orthogonal to brick.
The numbers that decide
For each candidate template, compute: mean fold in the full-fold area; fold sigma (uniformity); offset histogram standard deviation; azimuth aspect ratio (near/far azimuth spread ratio). Orthogonal typically scores ≈ (40, 5, 50, 0.6); brick ≈ (40, 3, 40, 0.65); zigzag ≈ (40, 8, 60, 0.3). Higher-fold-σ means more bin-to-bin variation, which shows up as amplitude stripes in the final section.
References
- Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.
- Vermeer, G. J. O. (2002). 3-D Seismic Survey Design. SEG Geophysical References 12.
- Stone, D. G. (1994). Designing Seismic Surveys in Two and Three Dimensions. SEG Geophysical References 5.
- Vermeer, G. J. O. (2012). 3D Seismic Survey Design (2nd ed.). SEG.