NORSAR has introduced two important additions to its traditional ray-trace modelling approach:
- Kirchhoff modelling
SimPLI is a patented method for fast, target-oriented, simulation of PSDM seismic sections.
Kirchhoff modelling is an extension to the conventional ray-tracing. It includes diffractions, which are beyond the limits of conventional ray modelling techniques.
These methods employ two different subsurface models, which are of different character:
- The target model
- The background model
The target model is the model of the target area in focus, often a reservoir.
The background model, also called the overburden model, is used for the ray propagation between the survey and the target area. The target model can be very detailed, while the background model must respect the assumptions and limitations set by the ray-tracing theory.
NORSAR is conducting research on how to prepare the optimum combination of target and background model. The research topics include:
- Preparation of the background model for ray-tracing. The original overburden model may contain large velocity contrasts and rough interfaces, while the ray-tracing theory requires a smoother model. The model must be smoothed, but key propagation properties, in particular the travel times and the ray directions at the target, should be well preserved.
- Combination of target model and background model. The background model is not only used above the target area, but also for ray propagation from the overburden and into the target area. The "split" of model properties in the target area between the background model and the target model is investigated.