Model verification

From SEG Wiki
Jump to navigation Jump to search
Seismic Data Analysis
Series Investigations in Geophysics
Author Öz Yilmaz
ISBN ISBN 978-1-56080-094-1
Store SEG Online Store

The final stage in earth modeling and imaging is the verification of the accuracy of the model itself (model updating). For an earth model in depth to be acceptable, it has to pass the following two tests:

  1. Image gathers from prestack depth migration using the earth model in question must exhibit flat events (Figures 10.1-10a and 10.1-11a). Events associated with multiples and converted waves (4-C seismic method) are not expected to be flat. Nevertheless, even with good models, usually, there also are some primary events that do not meet the flatness criterion. Violation of this criterion may occur because of erroneous layer velocities or 3-D effects that are not accounted for by 2-D modeling and imaging. Other sources of departures from flatness include strong lateral velocity variations that are much less than a cable length and effect of anisotropy on layer velocities.
  2. For an earth model in depth to be an acceptable representation of the subsurface geological model, it must be consistent with the seismic data used to estimate the model in question. To check for consistency, perform ray-theoretical modeling of zero-offset traveltimes associated with the layer boundaries included in the model (Figure 10.1-14). Then, superimpose the modeled traveltimes on the CMP-stacked section and observe any discrepancy between the modeled and the actual traveltimes (Figure 10.1-15). Here, we are assuming that the reflection traveltimes observed on a CMP-stacked section can be closely approximated by two-way zero-offset traveltimes. Actual traveltimes interpreted from the unmigrated CMP-stacked section are shown in Figure 10.1-3.

Aside from these two criteria, the estimated earth model needs to be validated by examining it for consistency with the structural model applicable to the area of interest. For instance, the faulting and folding implied by the the model must have the same patterns as in the true subsurface situation. Calibration to well tops is also part of the model validation procedure (model building).

See also

External links

find literature about
Model verification
SEG button search.png Datapages button.png GeoScienceWorld button.png OnePetro button.png Schlumberger button.png Google button.png AGI button.png