Exploration Geophysics - Volume 39, Issue 4, 2008

Various rules-of-thumb (e.g. Fresnel radius, Rayleigh limit) are commonly used to predict seismic resolution, based on the dominant frequency on the image. However, seismic resolution ultimately depends on more fundamental parameters including survey design, source bandwidth, geology, and data processing. A more instructive analysis is possible via numerical modelling of the acquisition process. Here we demonstrate the improved insight available with this approach, using examples taken from the petroleum and coal sectors.

We use viscoelastic finite-difference modelling to simulate 2D multi-component acquisition sequences. The ability to allow for anelastic attenuation is important as it permits a more realistic comparison of the resolution achievable on P-wave and converted-wave (PS) imagery.

An examination of vertical resolution for a wedge model on a petroleum scale indicates that processed P-wave sections have poorer resolution (62 m) than predicted by the Widess (20 m) and Rayleigh (40 m) resolution limits. For this model the vertical resolution for the PS data is comparable to that of the P-wave data. This is in agreement with the theoretical relative-resolution relationship.

A second example examines detection of lens-like features at petroleum depth. The resolving ability on the P-wave imagery is broadly consistent with analytical predictions appropriate to migrated data (100 m laterally and 40 m vertically). Again PS resolution is comparable to P resolution.

Analysis of a typical coal target suggests that barren-zones of width 5–10 m can be resolved. The interplay of wavelength and attenuation is such that the PS image is likely to exhibit comparable, or slightly reduced, lateral resolution, provided statics are not a problem. Resolution can be downgraded significantly if statics are more severe, and in practice this is likely to have greater impact on the PS image.

Realistic numerical modelling, simulating the full acquisition and processing sequence, leads to a more pragmatic understanding of seismic resolution issues. It is a valuable tool for survey planning and image interpretation.