Volume 5, Issue 2
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397


Separation of the upgoing and downgoing waves is a crucial step in the processing of Vertical Seismic Profiles (VSPs). There are many theoretical approaches to the problem but all so far published rely on a discernible separation between the two wavetrains in either the time-depth (t-z), frequency-wavenumber (w-k) or intercept time-slowness (t-p) domains. In the presence of very steep dips, for example when a well is close to a salt wall or diapir, or a near vertical fault plane presenting a high-impedance contrast, the angle of incidence of the reflected upgoing wave can be so close to the downgoing wave that both are removed by implementation of the velocity filters in current use. A practical method is described here for by-passing this failure of velocity filters in such situations. The method is an extension of the wavefield subtraction technique, described elsewhere in the VSP literature, and is illustrated by a recent case history. However the implementation of the method requires geological insight into the specification of probable models by means independent of the VSP. As such this illustrates the increasing need for synergism between the interpretation and processing teams.


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  • Article Type: Research Article
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