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Seismic Resolution of Zero-Phase Wavelets R. S. Kallweit and L. C. Wood Amoco Houston Division DGTS January 12, 1977 This PowerPoint version of the material, was compiled by Greg Partyka (October 2006) G. Partyka (Oct 06)

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Quiz Given: –Seismic section whitened between 5Hz and 60Hz –11ms measured two-way interval time –18,000ft/sec interval velocity of bed Find the thickness of a carbonate encased in shale: –99ft –49.5ft –18ft –any one of the above –none of the above Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Quiz Define the ormsby wavelet (f1-f2-f3-f4) that has the same resolving power as a 65Hz Ricker wavelet. – – – –all of the above –roll on your own: __-__-__-__ amplitude frequency f1 f2f3 f4 Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Summary Temporal Resolution: –The time interval between the wavelet’s primary lobe inflection points –The minimum two-way time through a thinning bed as measured on a seismic trace. Different types of zero-phase wavelets may be compared in terms of temporal resolution. The ability of zero-phase wavelets to resolve thin beds can be separated from variations in side-lobe tuning effects. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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What are the Limits of Temporal Resolution? As interval times through a thinning bed becomes less and less, how accurately do the measured times represent the actual, vertical two- way travel times through the bed? This questions may be further divided into two related questions: 1.How thin can a bed become and still be resolvable? In other words, when is the measured interval time essentially the same as the true interval time? 1.What are the errors between the true interval times and the measured interval times through thick beds? Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Why Zero-Phase? The use of wavelets that are not zero-phase greatly complicates the analysis of seismic resolution. The use of zero-phase wavelets simplifies resolution because traces containing zero-phase wavelets will have seismic interfaces located in general at the centers of the peaks and troughs of the trace (neglecting tuning effects and noise). Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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A Historical Perspective Since past work on the subject of seismic resolution is considered by many investigators to be definitive, new concepts and results will be examined carefully and compared with those in the literature. –We begin our study in the field of optics by examining the Rayleigh criterion of resolution, –We consider next a resolution criterion developed by Ricker (1953), and finally –We consider the criterion established by Widess in 1957 and published again in Geophysics in In each case, the theoretical limits of resolution will be related to parameters that can be measured on the wavelet that is convolved with the reflectivity sequence. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Rayleigh’s Criterion Optical diffraction patterns caused by light transmitting through a narrow slit may seem far removed from seismic resolution. It establishes a criterion of resolution which is often cited by many investigators in regard to seismic wavelets. Rayleigh’s work relates to resolution of two diffraction patterns. Two wavelets are resolved when their separation is greater-than or equal-to the peak-to-trough time of the convolving wavelet. The text book “Fundamentals of Optics” by Jenkins and White (1957) is a good reference. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Rayleigh’s Criterion Rayleigh chose to keep the mathematical relationships involved simple. When applied to wavelets other than sin 2 x / x 2, the “dimple-to-dimple” amplitude ratios may vary. b sin 2 x x2x2 b A 0.81A Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Ricker’s Criterion A bed, represented by two upright polarity spikes convolved with a wavelet, reaches the limit of resolvability when the bed becomes so thin as to cause a flat spot to appear in place of the two maxima. This occurs a a spike separation interval that can be derived equating to zero the second derivative of the convolving wavelet. This observation was made first by Ricker in his classic paper “Wavelet Contraction, Wavelet Expansion, and the Control of Seismic Regulation” by Norman Ricker (1953) Geophysics, Vol. 18, No. 4, p Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Ricker’s Criterion Ricker also recognized that as a bed, represented by two spikes of equal amplitudes but opposite polarities, becomes thinner and thinner, the complex waveform produced by convolving the spike pair with a wavelet looks more and more like the time derivative of the convolving wavelet. It was left to Widess to expand on this concept further in his paper: “How Thin is a Thin Bed” by M. B. Widess (1973) Geophysics, Vol. 38, No. 6, P Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Ricker’s Criterion b b A a7R Rayleigh’s CriterionRicker’s Criterion Flat d 2 (K t ) dt 2 0 = Y(f) = f f1f1 2 e 1 - (f/f 1 ) 2 “Wavelet Contraction, Wavelet Expansion, and the Control of Seismic Regulation” by Norman Ricker (1953) Geophysics, Vol. 18, No. 4, p Relates to resolution of two “Ricker” Wavelets. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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The Widess Criterion Widess considered a thin bed as one where the complex waveform across it does not differ significantly from the derivative of the convolving wavelet itself. This definition is useful for thin bed “detectability” studies, but causes problems when it comes to thin bed “resolvability” considerations. At the bed thickness Widess first considers a bed to become a “thin” bed, i.e., when the bed thickness is about /8; the apparent thickness is actually /4.6 which is the peak-to-trough time of the derivative of a Ricker wavelet. J. Farr in his paper: “How High is High Resolution (1976) SEG Preprint, states that a bed as thin as /40 may be detectable. It should be understood, however, that the apparent thickness remains at /4.6. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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The Widess Criterion The complex waveform across a thin bed approaches the time derivative of the incident wavelet as the bed thins to zero thickness. Widess states, “A thin bed is one whose thickness is less than about /8 where is the predominant wavelength…” Comment: The minimum time directly measurable through a “thin” bed may be calculated from d 2 (Kt) / dt 2 = 0 For a Ricker wavelet then, a “thin” bed is one which has a thickness less than /4.6 “How Thin is a Thin Bed” by M. B. Widess (1973) Geophysics, Vol. 38, No. 6, P Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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The Widess Criterion (Kt) Thick Bed Sonic Log Thin Bed Sonic Log = “Predominant Period” 1 / = “Predominant Frequency”. Not to be confused with “Peak frequency”. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Kallweit and Wood Proposition We now propose a definition of seismic resolution, in context of thin bed resolvability that ties together both Ricker’s and Widess’ criteria and relates both of them to parameters that can be measured on the incident wavelet itself. In order to separate the concept of “resolvability” from the related concept of “detectability”, the term Temporal Resolution (T R ) will be used to denote resolvability. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution The term “temporal resolution of a zero-phase wavelet” may be defined as the time interval between the wavelet’s primary lobe inflection points. This time may be derived from the equation: d 2 (Kt)/dt 2 = 0 This is the minimum two-way time through a thinning bed as measured directly on a seismic trace. A wavelet’s inflection points are found by setting equal to zero the second derivative of the wavelet itself. “Peak frequency” (f 1 )is not to be confused with the term “predominant frequency” which is defined in the literature as the reciprocal of the wavelet’s breadth (T b ). Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution (T R ) of the Ricker Wavelet TbTb TRTR f1f1 frequency amplitude peak frequency: f 1 temporal resolution:T R = 1 / (3.0)f 1 wavelet breadth:T b = 1 / (1.3)f 1 peak-to-trough:T b / 2 = 1 / (2.6)f 1 relationship of T b to T R: T R = 0.43T b = 0.86T b / 2 K t = [ 1 – 2( f 1 t) 2 ] e -( f 1 t) 2 Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution in Relation to a Sinc Wavelet Let us now discuss temporal resolution in relation to the band-pass sinc wavelet. This wavelet represents the output of an amplitude whitening process such as programs DAFD and WELCON. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution Peak-to-trough separation (ms) or apparent thickness (ms) Model spike separation (ms) or actual thickness (ms) 8 Hz – 64 Hz Sinc Wavelet Peak Amplitude of Wavelet TRTR T b / 2 Peak-to-Trough Time Separation Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution of the Low-Pass Sinc Wavelet The low-pass sinc wavelet can be analyzed in terms of its mid frequency in order to establish a similarity to the analysis of the Ricker wavelet. A low-pass sinc wavelet is not realizable in actual practice because it has frequencies extending to zero Hertz; nevertheless, it is instructive to study this wavelet. Temporal resolution is established in terms of the maximum frequency, and results can be used in the discussion of the bandpass sinc wavelet. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution of the Low-Pass Sinc Wavelet TbTb TRTR fmfm frequency amplitude T0T0 f4f4 temporal resolution:T R = 1 / (3.0)f m = 1 / (1.5)f 4 wavelet breadth:T b = 1 / (1.4)f m = 1 / (0.7)f 4 peak-to-trough:T b / 2 = 1 / (2.8) f m = 1 / (1.4)f 4 1 st zero crossings:T 0 = 1 / 2f m = 1 / f 4 relationship of T b to T R T R = 0.47T b = 0.93T b / 2 K t = 2 f 4 sin (2 f 4 t) (2 f 4 t) Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution (T R ) of the Bandpass Sinc Wavelet The band-pass sinc wavelet is the difference between two (f 1 and f 4 ) sinc functions. the f 1 sinc function has negligible effect on the temporal resolution of the wavelet for band-pass ratios of 2-octaves and greater. The resulting ability to relate temporal resolution to the highest, and only the highest, frequency of a wavelet leads to some very useful and quite accurate approximations. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Non-Binary Complexity What is the effect on temporal resolution when the amplitude of the second spike of a set of alternate polarity spike pairs is varied. –temporal resolution decreases slightly and in fact approaches the peak-to-trough time of the convolving wavelet. This behaviour is due to the constructive interference of the main trough of the positive spike wavelet on the center lobe of the negative spike wavelet. Note also that the “pseudo-thinning” pocket just prior to temporal resolution, is enlarged. Application of these temporal resolution concepts is discussed in the attached report on “Designing Optimum Zero-Phase Wavelets”. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution (T R ) of the Bandpass Sinc Wavelet TbTb TRTR fmfm frequency amplitude T0T0 f4f4 f1f1 f4f4 f 4 sinc f 1 sinc band-pass sinc f m = (f 1 + f 4 ) / 2 f1f1 temporal resolution:T R = 1 / (1.5)f 4 ; 2 octaves (where f 4 / f 1.ge. 4) wavelet breadth:T b = 1 / (0.7)f 4 ; 2 octaves (where f 4 / f 1.ge. 4) peak-to-trough:T b / 2= 1 / (1.4)f 4 ; 2 octaves (where f 4 / f 1.ge. 4) 1 st zero crossings:T 0 = 1 / (2f m ); all octaves relationship of T b to T R :T R = 0.47T b = 0.93T b / 2 ; for sincs.ge. 2 octaves T R of sinc and Ricker wavelets are equal when f 1 (peak frequency Ricker) = f 4 (sinc) / 2 K t = 2 f 4 sin (2 f 4 t) (2 f 4 t) 2 f 1 sin (2 f 1 t) (2 f 1 t) - Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Sinc Bandwidth and Temporal Resolution with Constant f max peak-to-trough separation (ms) spike separation (ms) 2–64 Hz Sinc (5 octaves) TRTR peak-to-trough separation (ms) spike separation (ms) 16–64 Hz Sinc (2 octaves) TRTR Conclusion:Temporal Resolution is the same for all sinc wavelets of 2 octaves and greater bandwidths having the same f max T R = 1 / (1.5)f max Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution (T R ) for All Band-Pass Sinc Wavelets Resolution constant (C) octaves T R for all band-pass sinc wavelets f 4 / f T R = 1 / C f /2 ms dT R for 64 Hz f 4 T R sinc = T R 4-64 sinc within 1/2 ms Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Temporal Resolution (T R ) with Spike Pairs of Unequal Amplitude peak-to-trough separation (ms) spike separation (ms) TRTR 16-to-64 Hz 2-octave sinc wavelet convolved with alternate polarity spike pairs of unequal amplitude Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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Next? Application of these temporal resolution concepts. “Designing Optimum Zero-Phase Wavelets”. Seismic Resolution of Zero-Phase Wavelets, R. S. Kallweit and L. C. Wood, Amoco Houston Division DGTS, January 12, 1977 G. Partyka (Oct 06)

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