b'Seismic windowSeismic windowMichael MicenkoAssociate Editor for Petroleummicenko@bigpond.comFootprint removalMost of us are familiar with an acquisition footprint in our seismic data. It is usuallyFigure 1.Horizon slice showing strong amplitude striping.seen as a variation in amplitude, or striping, which runs parallel to the recording direction and is caused by changes in number, azimuth and offset of traces that contribute to the stacked trace. An example of acquisition striping is shown in Figure 1.It is relatively easy to remove this striping in most situations if we can somehow estimate the amplitude variations. One way to do this is to measure the variation in the data and apply a correction. In many cases the overburden consists of sediments that have relatively constant properties; such as shales. So, if amplitude variations are seen in this part of the sedimentary column, they canFigure 2.Estimate of stripingaverage amplitude in a 400 ms window section above the target horizon.be assumed to be the acquisition footprint (Figure 2).To remove the acquisition footprint, the estimated footprint is used to normalise the extracted amplitude at the target horizon. The result should be a stripe free amplitude map as seen in Figure3. Although the striping is not totally removed it is reduced enough to identify the edges of the amplitude anomaly. If there is no constant property shale in the overburden then a good result can be obtained by calculating the average amplitude or RMS amplitude in a large window (say 500ms) above the target horizon and using that to normalise theFigure 3. Normalised amplitude at the target horizon. The footprint has been reduced and the edge of target amplitudes. the amplitude anomaly (blue) is more continuous.APRIL 2019 PREVIEW 36'