- Copyright © 2002 Society of Exploration Geophysicists
It is well known that a complex near surface—encountered in areas such as desert, mountainous, and glacial till environments—can significantly distort primary reflections from deeper horizons of interest. This has been and remains a major problem in seismic data processing.
One way to address this situation is via data processing methods that can be classified under the general term “redatuming” techniques. Conventional redatuming methods involve applications of static time shifts to the input traces. These time shifts (commonly known as statics) can be applied prestack and/or poststack to compensate for the effects of the near surface. The key assumption inherent in these conventional approaches is that the near-surface raypaths are nearly vertical. This implies a rather simple velocity distribution in the near surface. For a complex near surface, however, the vertical raypath assumption is not valid and conventional statics will introduce uncertainties in the interpretation of deeper horizons.
In this article we propose a novel approach to redatuming prestack seismic data. This scheme is fully data driven and firmly rooted to the principles of common focus point (CFP) technology. The advantage of this methodology is that a velocity macromodel for the near surface is not required. Instead, the effects of the near-surface are described in terms of propagation operators. These operators can be easily updated based on the “principle of equal traveltime.” Using the updated operators, a complete wavefield redatuming can be applied to the data by defining one subweathering reflector as the new acquisition surface.
According to CFP technology, migration can be formulated as a cascade of two focusing steps: focusing in emission and focusing in detection. Focusing in emission combines shots so that the simulated source array is focused at a specified grid point of the subsurface. The response is called a CFP gather. A CFP gather for …