Reverse Time Migration (RTM)
Reverse Time Migration (RTM) is a pre-stack two-way wave-equation migration algorithm-solution suited for imaging in areas of complex structure, being able to handle steep structural dips and high velocity contrasts (salt basins).
Spectrum is using the Paradigm™ Echos™ RTM algorithm package. Paradigm RTM is driven by velocity models developed with and refined using the GeoDepth velocity modeling tools.
Along with migration, we are utilizing forward modeling from the same Echos™ RTM package. Numerical seismic modeling presents an important part of seismic exploration workflows as it helps us better understand data, models and algorithms through controlled seismic experiments.
“BEFORE” = Velocity model used for modeling and migration (SEAM Phase I model, courtesy of SEAM corporation)
“AFTER” = RTM forward modeling and migration – RTM stack image (SEAM Phase I model, courtesy of SEAM corporation)
Kirchhoff Pre-Stack Depth Migration
Kirchhoff Pre-Stack Depth Migration (Pre-SDM) is the most commonly used pre-stack migration algorithm and it is well suited for moderately complex geology settings. The algorithm handles steep dips imaging and produces common image gathers for further velocity analysis. Spectrum’s Kirchhoff algorithm is available in 2D and 3D, with VTI/TTI anisotropic ray-tracing and imaging.
The method uses pre-computed travel time maps that are computed from surface positions to a grid in the subsurface for migration of the data. Travel times are computed for each point at the surface to a point in the subsurface for one ray path. This travel time may correspond to either the ray with the shortest travel time or the ray with the maximum energy. Ray trace travel times are also available. Typical parameters to test prior to running a production Kirchhoff migration include the aperture, the dip limits, the anti-alias filter etc.