Top 10 tips on effective use of seismic amplitudes
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This document provides 10 tips for using seismic amplitudes in reservoir characterization. It notes that amplitude is an interface property representing impedance contrast rather than directly responding to reservoir properties. Some key tips include using extremum amplitude values rather than averages, normalizing for background, analyzing regions above tuning thickness, and calibrating amplitudes with well data. The document aims to clarify misunderstandings around seismic amplitude analysis for improved reservoir characterization.
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Top 10 tips on effective use of seismic amplitudes
- 1. TOP 10 TIPS ON USE OF SEISMIC AMPLITUDES FOR RESERVOIR CHARACTERIZATION RajeshwaranDandapani,DirectorGeophysics rajesh@telestoenergy.com Introduction: Seismic amplitude analysis plays an important role in optimum reservoir characterization. People talk of so many fancy derived attributes and their uses now-a-days but sometimes fail to use the basic measured attribute called amplitude in an optimum manner for reservoir characterization. The main reason for this is because of lack of proper understanding of whatthat amplitude represents in terms of reservoir characteristics. First and foremost, mistake made by many is to think that the amplitude is the direct response of the reservoir. Amplitude is an interface property which tells about the impedance contrast between 2 layers (overburden and reservoir). The amplitude can vary if the reservoir varies or the overburden varies. Hence amplitude normalization with background is an important step before carrying out any meaningful analysis using amplitudes. Second common mistake made by many is to arrive at some relationship between a reservoir parameter like thickness, porosity, saturation etc and amplitude through cross-plot. I don’t say cross-plotting is bad. My only request is to understand that seismic amplitude is the combined response of all the reservoir parameters put together. Hence it is better to cross- plot Net Pay Thickness or Net Pore Volume and amplitude rather than individual parameters. I think with this introduction we are ready to go to the tips straight away. Tip-1: Use the extremum amplitude value like maximum or minimum instead of averageor RMS since extremumis the close representation of reflection coefficient at any interface. Average and RMS values over a window length are contaminated with unwanted wavelet overprint Tip-2: Use the formula(ReservoirTop Amplitude +Reservoir base Amplitude)/2 to minimize the bias created due to Coarsening and Fining upward sequences.
- 2. Tip-3: The window that is used for calculating the background amplitude should be sufficiently long in the immediate overburden of the reservoir (Clue: The amplitude distribution of background window should be close to Gaussian distribution) Tip-4: Perfect Zero Phased data is ideal for amplitude studies as it is the true representation of Impedance contrast but if not possible then the next best is to use the complex trace attribute (Amplitude Envelope). {Complex Trace Analysis is often mystified by some Geophysicists who appreciate only the mathematics without understanding theunderlying physical significance}. I will deal with that in detail in a dedicated article to demystify Complex Trace Analysis. Tip-5: Find out the Tuning Thickness of the reservoir by Wedge Modeling and carry out the Amplitude Analysis only in the regions where the reservoir is well above Tuning Thickness. Tip-6: You can study the sensitivity of one particular reservoir parameter to Amplitude provided you choose regionswhereyou aresurethat all the other parameters are more or less constant. Tip-7: Always use the Interval Average value when analyzing inversion products like (Acoustic Impedance, Elastic Impedance, Vp/Vs ratio etc.,) since they are elastic properties representative of layers unlike amplitude which is an interface property. Tip-8: Use at least 16 bit data to get reasonable results through amplitude analysis. 8-bit data is good only for structural interpretation. Please do not use it for amplitude analysis. Tip-9: When dealing with amplitudes pertaining to different vintages it is better to evaluate a quantity called percentage ratio of anomalous amplitudes to background which can minimize the disparities introduced due to dissimilar acquisition and processing parameters. Tip-10: Seismic to Well matching when done carefully can providegood calibration of amplitude with actual reflection coefficient. Theseare a few tips which cameto my mind as of now. I amopen for further discussion and further detailing depending on the interactions from the esteemed LinkedIn members. Telesto Energy Pte Ltd, #30 Cecil Street, #19-08, Prudential Towers, Singapore – 049712 contact@telestoenergy.com www.telestoenergy.com