Binning QC and coverage maps

Part 6 — QC during acquisition

Learning objectives

Read a daily fold map: identify holes, edges, and uniform centre
Quantify fold uniformity with CoV and low-fold percentage
Plan infill shots to repair cold patches before demobilisation
Recognise the cost of late detection: role="main" aria-label="Lesson content" tabindex="-1"00k+ re-mobilisation

The coverage map is the single most-read daily deliverable of any survey. At the end of each shooting day, the crew plots fold-per-bin as a heatmap over the image area. A healthy survey shows a warm uniform centre with cool tapered edges; an unhealthy one shows cold patches in the interior, corresponding to obstacles (roads, towns, rivers), broken stations, or skipped shots that never got repeated.

Reading the map

Three features to scan for. The centre should fill to nominal target fold (typically 30–60 for 3D exploration; 100+ for dense reservoir 3D) in a uniform warm colour. The edges taper down gradually as the roll-along leaves the template; this is expected. Any cold patch in the interior is a problem: a fold hole that will be a black spot in the stacked section unless repaired.

Quantifying uniformity

Two numbers drive decisions. Coefficient of variation (CoV) across interior bins (ratio of std-dev to mean fold): target CoV ≤ 20% at final day; above 30% means the image will have patchy S/N. Low-fold percentage (fraction of interior bins under 80% of nominal): target ≤ 5% at final day; above 10% means measurable imaging gaps.

The infill plan

Detected cold patches are repaired by an infill shot plan: a list of extra shot positions, usually on displaced or re-permitted ground near the obstacle, fired in the last few days of the crew’s deployment. A well-run crew schedules 5–10% of total shots for infill from day one; an unprepared crew discovers the need for infill too late and has to re-mobilise. Re-mobilisation of a departed crew typically costs $100k–$ 500k for a regional survey and several months of schedule.

QC cadence

Industry rule: the coverage map is updated every day, reviewed every day. A one-day delay in finding a fold hole is acceptable; a one-week delay can mean the crew has moved out of infill range. Many clients require the crew to submit the coverage map to HQ within 12 hours of the day ending.

References

Vermeer, G. J. O. (2002). 3-D Seismic Survey Design. SEG Geophysical References 12.
Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.
Bouska, J. (1995). Cube management — 3D acquisition design. The Leading Edge, 14(1), 53–57.
Stone, D. G. (1994). Designing Seismic Surveys in Two and Three Dimensions. SEG Geophysical References 5.