The advent of high channel count recording systems, high-productivity vibroseis techniques and advances in wide-azimuth processing, means onshore 3D seismic is undergoing a revolution. This revolution is the move from sparse to high-density WAZ acquisition with finer sampling, and it is being made possible by high-specification 'SuperCrews'.
Onshore 3D surveys have generally been limited to sparse wide-azimuth geometries for both technical and economic reasons.
At times, typical land seismic data have been poorly sampled and noisy. As a result, image quality has been poor compared to marine seismic, despite the wide-azimuth geometry.
Today things are very different.
CGGVeritas 'SuperCrews'
CGGVeritas is at the forefront of high-density land WAZ acquisition, with two high channel 'SuperCrews' currently in operation in the Middle East. These CGGVeritas SuperCrews are recording data at up to 100 times the density of conventional land surveys. Remarkably, this makes the new-generation land acquisition sampling finer than current marine WAZ surveys by a factor of 10.
It is important in the onshore environment to ensure that the seismic wavefield (including signal and coherent noise) is adequately sampled, so that the full benefits of wide-azimuth techniques can be realized through the latest WAZ land processing.
|
Reference |
CGGVeritas 1 |
CGGVeritas 2 |
| Receiver grid (m) |
250 x 50 |
200 x 25 |
120 x 7.5 |
| Source grid (m) |
200 x 50 |
50 x 50 |
90 x 7.5 |
| Bin size (m2) |
25 * 25 |
12.5 * 12.5 |
3.75 * 3.75 |
| Aspect ratio |
0.3 |
0.8 |
0.83 |
| Live channels |
3,840 |
10,560 |
24,000 |
| Fold |
240 |
1,320 |
504 |
| Traces / km2 |
384,000 |
6,400,000 |
35,840,000 |
* Aspect ratio of receiver spread with 1 indicating a WAZ geometry with equal inline and crossline dimensions.
|
High Channel Count Benefits
- Improved noise and multiple attenuation
- True 3D wide-azimuth algorithms
- High-resolution velocities and statics
- Azimuthal velocity analysis
- Wide-azimuth illumination of targets
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