Low Frequency Specific Matching

Deterministic signature deconvolution is routinely applied to the surveys that comprise a marine time-lapse project. The process replaces the source wavelet of each survey with a common target wavelet, simultaneously deconvolving the data for the source bubble. Occasionally the farfield signature, from which the designature operator is computed, does not accurately model the bubble generated by the source array, so that residual bubble energy remains. Although this may not be obvious on the individual seismic datasets, it can become visible as low-frequency residual energy on the 4D difference datasets and hamper time-lapse interpretation. WesternGeco has implemented “low-frequency specific matching” to address this issue. Applied as a frequency-variant global or local operator, the process matches one survey to another over the bandwidth affected by the residual bubble. All other frequencies are left untouched, thus minimizing the chances of affecting the time-lapse signal.