b'Seismic window Seismic windowFigure 1.Seismic line showing picked horizons A,B & C and nine stratal slices between A & B and one between B & C (right). Horizon overlays are Michael Micenkoremoved (left) to show some anomalous features of Associate Editor for Petroleuminterest in ellipses. Figure 3.RMS amplitude over the A2A3 micenko@bigpond.com interval. The enlargement clearly shows the small and polarity flips. Below that is acircular features.reflector that is broken up such that it Stratal slicing would be tricky to interpret across a large area. A similar interval is present Stratal slicing is a technique that fillsabout midway between reflector B & C. the gaps between interpreted horizonsUsing stratal slicing, amplitude maps of in a 3D seismic volume. It is describedeach can be quickly produced in order on the SEG web site as a proportionalto aid the geological interpretation of or linear slicing between two or morethe area.reference surfaces in a seismic volume.Stratal slice A2 does indeed have The aim is to improve the understandingseveral circular point features, perhaps of otherwise unclear or muddleddewatering mounds or debris from horizons. Many software packages willa meteor shower (Figure 2). These calculate the stratal slices and extractare difficult to see on the stratal slice amplitudes at the press of a button butamplitude map, so an RMS amplitude it is quite easy for those of us with deepwas calculated over the A2 to A3 interval pockets and short arms to do our ownto enhance the small circular anomaliesFigure 4.Amplitude of stratal slice A3 showing calculations (see box). (Figure 3). Layer A3 is quite differentseveral linear, equispaced, parallel northeast- and more interesting with several quitesouthwest channels. There is a large change Calculating stratal slices regularly spaced incisions or channelsin geology between this slice and the slice crossing the area from northeast toimmediately above (Figure 2).TWT (x) = TWT(A) + x (TWT(B)-TWT(A))/N southwest (Figure 4) and although Where x is the slice number from 1tothe reflectors look similar the stratal N and N -1 is the number of slicesamplitude at B1 has broader features between the horizons A & B trending northsouth (Figure 5).TWT is two-way timeHere is an example of stratal slicing in a simple setting in the Vulcan sub-basin of NW Australia (Figure 1). The geology appears quite simple with several continuous parallel reflectors. Three reflections (A, B & C) were picked across an area of interest and amplitude maps of these surfaces were quite boring with no obvious anomalies. TheFigure 5.Stratal slice B1 amplitude has several interval between A & B was dividedbroad features trending northsouth.into 10 layers while the B to C interval was divided into two layers usingFinally, congratulations to Tony Marsh of stratal slicing instead of picking eachChevron who was awarded the best oral layer by hand or auto-tracking. JustFigure 2.Amplitude of stratal slice A2. The pointpresentation at the AEGC conference last below Horizon A is a reflector whichfeatures seen on the vertical section (Figure 1) areSeptember for his presentation about has several points of high amplitudesubtle red spots. Stratal slicing.DECEMBER 2019 PREVIEW 48'