Velocity Estimation for Wave Equation Depth Migration
Accurate specification of interval velocity is key to the success of depth migration. It is no surprise, then, that most of WIT's energy in processing goes toward velocity analysis. Since 2008, we have filed two US Patent applications on velocity analysis technology.
WEM Angle Gather Update - WIT filed a patent in 2009 on a method to measure the 3D propagation direction of a wavefield in a one-way WEM algorithm, and then to use the propagation direction vectors for the source and receiver wavefields in a shot record WEM to determine incidence angle, azimuth angle, and dip angle. We've extended the technique to apply to RTM angle gathers.
We efficiently and directly form true angle gathers -- usually incidence angle gathers for the purposes of velocity analysis. WIT's method is vastly more efficient than many other methods in the literature. Running a WEM with angle decomposition produces a full volume of angle gathers. For instance, the user might desire incidence angles from 0 to 48 degrees, sampled at 4 degrees, or 12 angle volumes.
The full volume angle gathers can be analyzed for residual curvature and used to update the velocity. Currently, we perform a parabolic velocity scan on the gathers and apply a vertical velocity update. The vertical update method is suited to resolve velocity inversions and sharp boundaries in areas with high S/N and lots of usable reflectors.
This image depicts an RTM image overlain with the velocity field obtained by 8 iterations of WIT's angle gather update. WIT's workflows are able to resolve sharp velocity contrasts, both vertical inversions and lateral variations across faults, without burdening the client with the task of hand-picking faults and layers
Interested in reading more about WIT's velocity estimation technology?