b'Seismic window Seismic windowMichael Micenko Associate Editor for Petroleummick@freogeos.com.auFlat spots arent \x1cat1Seismic \x1cat spots are \x1cat re\x1cections on a seismic section and are potentialFigure 1.Screen grab of an example \x1bat spot (indicated with white arrows) from Brazil. The top of the indicators of hydrocarbons (Figure 1).hydrocarbon reservoir (white) and the base of the hydrocarbon column (black) are opposite polarity. They are usually \x1cat because they areImage provided by Jarrod Dunne and James Parsons.re\x1cections from a \x1cuid interface (such as gas over oil, oil or gas over water) within a petroleum reservoir (Figure 2). I have written about \x1cat spots in previous issues of Preview, however my focus on those occasions was on how to highlight and recognise \x1cat seismic re\x1cectors. But what if the re\x1cector is not \x1cat? An interesting presentation by Jarrod Dunne at the AEGC earlier this year explored the world of non-\x1cat \x1cat spots, with examples from a variety of settings and locations shallow gas hazards in Sakhalin, oil \x1delds in Brazil and gas-oil contacts in the Browse Basin of Australia. As it happens, non-\x1cat \x1cat spots are common enough for Jarrod to propose a more representative nomenclature for this type of direct hydrocarbon indicator (DHI). He would like us to stop calling them \x1cat spots and to use the term contact indicator.There are several reasons a contact indicator does not appear to be \x1cat, including hydrodynamic e\x1eects (Figure3), aquifer depletion prior to the seismic acquisition, semi-permeable barriers (Figure 4), and reservoir heterogeneity, but possibly the most common is variation in the seismic velocity of the overburden and the limitations in resolving the velocity. These limitations lead to explorers either misinterpreting \x1cat events as hydrocarbon contacts, or passing over a prospect by failing to recognise a rugose 1This article is based on a paper by Jarrod Dunne and James Parsons presented at the AEGC 2023 Figure 2.Another example of a contact indicator. Image provided by Jarrod Dunne and James Parsons.JUNE 2023 PREVIEW 28'