Results of development drilling on a North Sea oil field suggested that the actual structure was much more complex than the original interpretation. We present the results of a reprocessing project on selected seismic lines over the structure. The original data were recorded using a variable cable depth and a deep tow hydrophone for the gun signatures. The data were reprocessed using only signature correction to a zero-phase wavelet. However, results obtained at the horizon of interest were still affected by cable ghosts, frequency attenuation within the overlying sediments, and practical constraints on the recording of the source ghost.

Because the purpose of the project was to improve delineation of very small faults, we decided to try to improve resolution by applying corrections for these effects. The initial tests were done by designing and applying

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filters to the signature prior to the design of the wave shaping operators. We used an average cable ghost operator in this run and designed a single operator for each shot to enhance the wavelet in the zone of interest. The results were encouraging, so we decided to try removing residual effects in a separate pass on a trace-by-trace basis after the normal signature correction. The output obtained was disappointing; therefore, we decided to use prefiltering of the signature before operator design on a trace-by-trace basis.

This proved to be much less sensitive to noise on the input data and results show the small faults in the oil reservoir.

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