Simple versus complicated seismic processing in the Exmouth Sub-basin

Abstract

Seismic data quality in the deeper water regions of the Exmouth Sub-basin, Western Australia is generally excellent. Both the temporal and lateral resolution are very high, allowing the identification of fine geological detail. These data contrast with the data over much of Australia's offshore exploration and producing regions, where multiples, velocity inversions, poor reflectivity contrasts, and sea floor reefs and channels seriously degrade data quality. A quite different approach to seismic data processing is required for processing seismic data from the deeper waters of the Exmouth Sub-basin than is normally used for the more noisy areas of offshore Australia. Rather than concentrating on processes that improve the signal-to-noise ratio of the data, it is more important to concentrate on processes that do not distort the seismic wavefield. While processing seismic data recorded in 1994 in the Exmouth Sub-basin, I found that most processes typically applied to seismic data did not lead to any improvement in quality. In fact, it was quite difficult to find processes that actually improved the quality of the data. I found that the results of processing were very susceptible to the type of deconvolution applied to the data. Conventional trace-by-trace prestack deconvolution was found to introduce reverberations, degrading the quality of the final migrated section. Shot averaged deconvolution produced vastly superior results than trace-by-trace deconvolution. Other processes such as shot domain f-k filtering, trace summation and f-k demultiple had little effect on the quality of the final section. These processes, however, can introduce subtle distortions of the wavelet, and hence should only be used if it can be demonstrated that they produce noticeable improvements. The final sequence used to process the data was extremely simple, and consisted of: (1) gain recovery; (2) large gate trace equalisation; (3) shot averaged deconvolution; (4) one pass velocity analysis; (5) NMO, mute and stack; and (6) migration followed by bandpass filtering. Probably many of the deeper water regions of Australia could benefit from the use of the simple processing sequence presented in this paper.