b'Seismic window Seismic windowMichael Micenko Associate Editor for Petroleummick@freogeos.com.auReducing risk with seismic stratigraphyIn this issue I am returning to a prospect on Western Australias NW Shelf which was described in Preview Issue 220, October 2022. The prospect is assigned a high risk because it is a stratigraphic trap, which is more complex to describe and riskier than structural traps.Risk assessment is usually based on four or five risk elementssource,Figure 1.Environment of deposition map showing a number of overlapping lobes prograding to the NW. seal, charge, reservoir and trap. To beWell A is located on the distal fringe of a lobe which is more likely to be shale prone than the prospect area.successful a prospect needs to have all these elements in place. In this case the source, charge and seal are confirmed by surrounding wells and the trapping mechanism works in nearby discoveries where it is fairly well understood. So, the remaining risk is the presence and quality of reservoir rocks. And heres the crunchthe nearest well intersected poor quality reservoir rocks, and this has adversely affected the perceived prospect risk. However, the prospect has excellent 3D seismic coverage that can be used to reduce the reservoir risk by applyingFigure 2.Seismic dip line (A-A) across prospect (in the ellipse). The reservoir section thins to the NW some simple seismic stratigraphytowards Well A. Green arrows indicate the top reservoir unconformity. The box outlines the approximate principles to create an environmentarea shown in Figures 3 and 4.of deposition (EOD) map (Figure 1). The EOD map shows a number of fan lobes prograding to the north-west with Well A located on the fringe of the northernmost lobe. The prospect is situated in a location that is more proximal than Well A (4-5 km to the north).The seismic line in Figure 2 shows the reservoir section thins to the north-west largely due to erosion at the unconformity surface, but there is aFigure 3.Seismic dip line flattened on horizon below the base of the reservoir. Flattening the section component of thinning to the west withenhances the internal stratigraphic features of the reservoir. Down lap shown by yellow arrows.OCTOBER 2023 PREVIEW 32'