b'CommentarySeismic windowThe SEG positive polarity definition Seismic window makes sense because an increase in impedance produces a positive reflection coefficient which is displayed by a positive number or black peak. With this Michael Micenkodefinition the mathematics is consistent Associate Editor for Petroleum and AVO analysis and seismic inversion is E mick@freogeos.com.au simpler with no need to swap sign.But in Australia and Europe the opposite During the appropriately nameddisplay. This convention is called positiveconvention is often used. The correct Christmas break, I managed to fall onstandard polarity (an increase inname for this convention is SEG negative a concrete cricket pitch while bowlingacoustic impedance produces a positivestandard polarity, not ASEG polarity. to my seven-year-old grandson andreflection coefficient). There is also aThe SEG polarity standard is quite clear broke some bones in my hand. As adefinition for minimum phase waveletsand is illustrated below (Figure 1) along result, my keyboard skillsare somewhatbut I will stay with zero phase becausewith the polarity conventions used by compromised, so I have picked one ofmost seismic processing aims to outputan Australian operator, an international my favourite columns from the past fora zero phase waveleta symmetricaloperator working in Australia and a reproduction in thisissue. wavelet with a maximum value atEuropean service provider. To confuse zerotime. interpreters even further Operator A Since this article was first publisheddisplays AVO (Figure 2) and inversion in 2013 (Preview 163), I have notedThe SEG Dictionary also describes dualresults with the opposite polarity to an increase in the number of reportspolarity displays as Troughs may betheir display of standard seismic data. that include a section describing thecolored red and peaks blue or black, orThey do this to avoid the situation polarity of the seismic displays, whichsome other combination of colors mayshown in Figure3. Even industry leaders isencouraging. be used. This is more like a suggestionSchlumberger (2013) have no consistent but is an extension of the polarityusage, with their excellent web-based I hope you enjoy reading this blastdefinitionif the peaks are colouredOilfield Glossary correctly describing fromthe past! black a contrasting colour, commonlypositive polarity while their Petrel red, was used to colour troughs. software defaults to something else.The demise of ASEG polarityI would like to dispatch to the annals of history the term ASEG polarity or Australian SEG polarity when referring to seismic data displays. There is no ASEG polarity standard. Seismic data polarity is a common source of confusion for many interpreting geophysicists (Simm and White 2002), including me. As a joint venture representative, I attend meetings andFigure 1. The SEG positive polarity standard for zero phase wavelets. From left, an increase in acoustic presentations with several companiesimpedance produces a positive reflection coefficient that is displayed on wiggle variable area displays as and to fully understand the presentationa black peak or blue on a variable density colour display. The three right wavelets illustrate the variety of material it is necessary to confirm theconventions used by three companies operating in Australia. Only one uses the SEG standard.display polarity because it determines how an increase (e.g. intrusives) or decrease (e.g. gas sand) in acoustic impedance appears.The only definition of normal or standardpolarity I know is given in theSEG Encyclopedic Dictionary of AppliedGeophysics (Sheriff 2002). Here is an excerpt from the online version (https://wiki.seg.org/wiki/Dictionary:Polarity_standard), for a zero phase wavelet, a positiveFigure 2. Even companies with well-defined standards have internal variation. The Schlumberger glossary reflection coefficient is represented byof oil field terms (internet) correctly describes the SEG standard, but their interpretation software (Petrel) a central peak, normally plotted blackdefaults to something else. A major operator uses SEG negative polarity for seismic displays but reverts to on a variable area or variable densitySEG positive polarity for QI and AVO displays.FEBRUARY 2024PREVIEW 37'