Wave field modeling and Demigration*
Wavefield modeling is an important task that appears at different stages of seismic processing. This is clear if we keep in mind that the final task of processing and interpretation is closely related to the reconstruction of physical characteristics of the real medium from the measured wavefield. How to check the correctness of the obtained solutions? The representation of the obtained medium parameters into the real observations is a necessary indication of the reliability of solutions.
However, the verification of validity is only a single and not the most popular application of the wavefield modeling technique.
The most traditional application of modeling is the planning of observations. In this task, however, it is usually limited to ray modeling. This is often all that is needed. However, when it comes to identifying processing and interpretation opportunities that rely on dynamic features of the data, a more sophisticated toolset that allows modeling of more realistic wavefields is needed.
What else does modeling allow you to do?
To check the real possibilities of certain processing and interpretation software. Selection & adjusting of procedures parameters, identifying of distortions introduced by them and, in some cases, compensation of these distortions. Finally, modeling of wavefields allows to identify those attributes obtained during processing and interpretation, which allow to reliably identify objects of interest to the geologist.
In the Prime software, tools for modeling seismic wave fields are realized in the form of separate modules and plug-ins.
For kinematic modeling, ray-tracing techniques are provided, as well as a continuation in time of kinematic wave-field fronts.
Combined techniques are used to perform dynamic modeling:
1. Transformation of the wave fields on the basis of recalculation of the field from the boundary to the boundary of the acoustic impedance discontinuity of Velocity-Depth Model by Kirchhoff-type transfer operators. These transfer operators can also use the linear absorption parameters of the medium. Here, it is also possible to use a specialized anti-aliasing scheme.
2. Kirchhoff Migration Operator Reversal Techniques (Demigration).
3. Construction of hybrid solutions on the basis of calculated local seismograms by finite-difference methods on the top of the target layer, with subsequent polarization filtering of waves of desired polarization type and transfer of the obtained fields to the observation geometry.
An important feature of modeling, both kinematic and dynamic, is the indication of the 'wave code', according to which the desired element of the wave pattern is calculated. I.e., based on the boundaries of the Velocity-Depth Model, it is determined what should occur to the field after reaching the field front of this boundary - reflection/propagation, perhaps, a change in the type of wave polarization.
Except for the construction of hybrid solutions based on the usage of local seismograms computed by finite-difference methods on the top of the target layer, the response function of the medium to the source function is determined based on the asymptotic Born approximation. Thus, the dynamic parameters of the wave field are formed based on the same models that are used in the solution of inverse dynamic problems (dynamic inversion). This is true both for the Boundary-Integral modeling of reflected waves from the Velocity-Depth Model boundaries and for the Kirchhoff migration operator inversion technique (i.e., the demigration method).
As a rule, in the industry, the task of modeling wave fields is a valuable, in some way an exploratory one, to verify the possibilities of a particular seismic processing graph in particular seismological conditions:
1. in terms of structural constructions;
2. in terms of preservation of dynamic parameters of the wave field for the purpose of subsequent solution of inverse dynamic problems.
However, some of the tasks of the seismic data processing itself clearly require the presence of a prototype of useful reflected waves on the observation geometry, i.e., benchmark gathers. Such gathers in the process of seismic data processing are formed at various stages of Velocity-Depth Model creation by means of a special case of the modeling tools usage - Demigration.
For more details on wavefield modeling and demigration, please use the links.
These solutions are included into the following software tools: 2D module - Bidatuming, plugins for 3D - Kinematic+Amplitudes Modeling 3D and BI-WFT 3D Cluster.
Software solutions are fully ready for commercial usage and tested by us on a number of commercial projects – please find our articles .
Software solutions may be tested and purchased by filling out an application form
*These solutions are represented as standalone modules, integrated into the Prime software, they are licensed separately.
