In many situations, the un-migrated time image itself can be regarded as a by-product, and the improved prestack seismic traces with increased signal-to-noise ratio are requested. Typical examples of such situations are velocity model-building or prestack time or depth migrations. Both MultiFocusing versions: ZOMF and COMF can be used for this purpose. But the global, quasi-hyperbolic zero-offset operator used in ZOMF method limits the efficiency of this application for cases of complex geology and/or strong lateral velocity variations. In these cases, the traveltimes of seismic events become non-hyperbolic and ZO-MF (or CRS) operator approximation starts to be inaccurate. Similar effects can be caused by anisotropy or large offsets.
The procedure used to create pre-stack seismic data with enhanced signal-to-noise ratio has several versions for different seismic data and MultiFocusing types. This done by partial stacking of the pre-stack data in some vicinity using optimal parameters of the MultiFocusing extracted from pre-calculated database of same MultiFocusing and seismic data type (ZOMF or COMF, 2D or 3D).
This procedure can be used for data regularization due to the fact that MultiFocusing approach doesn’t required CMP symmetry and time correction can be calculated for free imaging point within the acquisition.
The algorithm for data enhancement can be described as follows:
According to estimated MF parameters, the partial MF stack calculates a stacking surface around a specified CMP-offset location, and performs the summation of data along that surface. The result of summation is assigned to the same CMP, offset, and time coordinates. Repeating this procedure for all desired points generates a new gather that is called the MF enhanced supergather. Figures 2 and 3 illustrate the proposed data enhancement idea. The original common super-shot (Figure 2a) has low signal-to-noise ratio and is characterized by a complex kinematics of reflection events due to the surface topography and subsurface geology. The MF enhanced gather (Figure 2b) shows essential signal-to-noise improvement, and it preserves all main kinematic and dynamic features of the original data. Velocity analysis performed on the enhanced gather (Figure 3b) is cleaner with better definition of the primary reflection event compared to velocity analysis using the original data (Figure 3a).
Input data –
oMF database (ZOMF or COMF, 2D or 3D)
oPre-stack data
oOutput geometry
Output data –
oMF-enhanced pre-stack data
There are few available data enhance modules:
oData Enhance - 2D ZO-MF
oData Enhance - 2D CO-MF
oData Enhance - 3D ZO-MF
oData Enhance - 3D CO-MF
