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Sub-basalt imaging continues to provide a challenge within the West of Shetland region. Successful imaging is being achieved through the reprocessing of 2D reflection seismic data. These were acquired with conventional source array and streamer parameters and include key signal processing techniques. The first technique involves spectral processing to boost lowfrequency signals at the early stages of processing. The second technique involves attenuating coherent and incoherent noise in all of the available 'time-offset' domains. Examples of the data after application of these techniques are presented and clear improvements over the original processing are demonstrated. As work on these reprocessing methods has progressed, the benefits of moving to a true broadband processing solution have become clear.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

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Extensive sequences of flood basalts dominate the northwest European Atlantic margin. The basalt flows absorb and scatter the higher frequencies present in any source wavelet through intrinsic and apparent seismic attenuation. Successful sub-basalt imaging therefore tends to focus on the generation of low frequencies in acquisition and retention in processing. Conversely, the Rosebank discovery in the Faroe-Shetland Basin of oil bearing sequences interbedded within the Basalt illustrates that high frequencies need to be recovered in order to delineate subtle stratigraphic plays. For this we require broad bandwidth, a robust approach to signal to noise improvement and accurate knowledge of the seismic quality factor (Q) to compensate for locally strong attenuation effects. We show that the required bandwidth can be obtained from conventionally acquired seismic data through the use of low and high frequency boosting operators and application of a horizon consistent Q field. The latter is derived using the pre-stack Q-inversion (PSQI) method to determine effective Q in defined intervals from the data itself. Through a combination of both techniques a substantial uplift in resolution is demonstrated for the highly prospective intra-basalt units with useable frequencies up to 50Hz.

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