Multiple attenuation: some current techniques

Abstract

Multiple attenuation techniques have to be based on some difference between the multiples and the primary reflections. The two major differences that are exploited are firstly velocity, and secondly the fact that multiples are periodic sequences of events, and hence are predictable, while the primaries are non-periodic. The widely used frequency-wavenumber (F-K) domain techniques rely on velocity difference only, but a recent variation of this method also makes use of any difference in dip between primaries and multiples to give significantly greater multiple attenuation. For short period multiples, velocity differences may be insufficient for much attenuation, and the process has to be based on the multiple's periodicity, using some type of long predictive deconvolution operator. One problem with this approach is that the multiple period varies with time, particularly at long offsets. Transforming the record to the tau-p domain removes this variation however, allowing more effective deconvolution of the multiples. Another recent approach is to model a multiples-only record by wave equation methods, and subtract it from the recorded data. At present however, this is limited to well defined multiple generators, such as the water layer. With the variety of multiple attenuation processes available today, the geophysicist needs to understand the types of multiple problem to which each is most suited, in order to select the technique most applicable to his data.