New Technology
Straight Ray Datuming - NEW to SpectrumThe conventional “statics correction” method to correct for time distortions introduced by the weathering layer has its limitations. It relies on assumed surface consistency, requires a vertical ray path and needs ray theory to be an acceptable approximation of near surface wave propagation. In the presence of rapid lateral variations of the weathering layer, one or more of these conditions are not met.
However, more advanced methods such as Kirchhoff Pre-Stack Re-datuming or finite difference for such corrections can also often be unfeasible. These methods can have a high computational cost and can also require highly rigorous, time consuming processing; and considerable sampling of the sources and receivers, not seen in conventional 3D land acquisition.
Spectrum can now provide an innovative solution to bridge the gap between these methods. Straight Ray Datuming (SRD) is a new advance in statics modelling developed for commercial use by Tariq Ali Alhalifah, a professor at King Abdulaziz City for Science and Technology University in Saudi Arabia. It was directly sponsored, supported and developed for commercial use by Spectrum.
Main advantages of this technique include the removal of a vertical ray path requirement. It allows time distortion corrections conducive to actual wave propagation and contains a lateral extension to consider the finite size of the Fresnel zone at the reflector. The technique has been proven to work on both 3D and 2D acquisition
As well as having provided an intermediate statics process, straight ray gives some additional advantages:
- More flexibility in acquisition - Can be applied to common shot gathers and common receiver gathers.
- Less input - SRD does not require detailed near surface velocity models, refraction static information or other common near surface time shift input.
- Irregular Sampling - SRD can also be used to spatially map irregularly sampled data into regularly sampled data at the datum
- Noise Reduction - As the process is a partial migration, it helps suppress diffractions generated from above datum inhomogeneities.
SRD kinematics are derived using geometrical optics. The figure above schematizes the rays involved in the SRD impulse response. SRD rays are selected to satisfy Snell’s law at the datum, so the impulse response depends on the velocity below the datum which can initially be set to an expected average value.
The application of Snell’s law at the interface allows the reduction of the surface integral, needed in Kirchhoff datuming, to a surface integral applied once (a stationary phase approximation). The trajectory of the summation operator depends on offset, elevation of the source and receiver, and the velocity of the weathering layer under each source and receiver.
