According to assumption 5, the seismic wavelet is always minimum phase, which is a causal signal and its energy is zero before time zero. This is why its necessary to filter the logs back to the resolution of the seismic. The zone is 5 msec thick, corresponding to 10m at 4,000 msec. A wavelet is a wave like oscillation with an amplitude that begins at zero, increases, and then decreases back to zero. The zero phase wavelet is also considered to have higher resolving power. An analysis of seismic wavelet estimation by ayon kumar dey athesis submitted to the faculty of graduate studies in partial fulfilment of the requirements for the degree of master of science department of geology and geophysics calgary, alberta november 1999 c ayon kumar dey 1999. Each of above created synthetic ricker wavelet is merged. When the estimated constant phase of the statistical wavelet is consistent with the final result, the wavelet estimation converges more quickly than when starting with a zero phase assumption. The vertical resolution box 1 is derived from the length of the sound wave. Physical seismic model experiments have been undertaken to study the detectability and lateral resolution of buried linear reflecting targets slits in an aluminium plate which might simulate a range of interesting geological structures, e. Figure 1 shows the workflow for the method outlined above. Hilterman, 1985 tom wilson, department of geology and geography the default wavelet in struct is the ricker wavelet.
Another goal of deconvolution is to produce a wavelet with a simple phase character, ideally a zero phase wavelet, which is the same for every trace in the seismic. Seismic source wavelet estimation and the random reflectivity assumption ayon k. Zero phase wavelets are symmetrical in shape about zero time whereas non zero phase wavelets are asymmetrical. When applied to a zero phase wavelet, this operator causes a 90degree phase shift. Phase in seismic data is simply known as the lateral time delay in the start of a reflection recording, and because it is amplitudeindependent, phase can be used as a good continuity indicator in poor reflectivity areas in the seismic data with a higher sensitivity to reflection discontinuity caused by pinch outs, faults, fractures, and other structural and stratigraphic seismic. Topics reflection and avo simple imaging concept of zero. This method attempts to reconstruct the form of the wavelet hampsonrussel software 1999. There are two types ricker wavelets are generated directly in the time domain and klauder wavelets are generated in the frequency domain. Not only in time domain but also in frequency, z, wavelet, complex hilbert and other domains. After the seismic wavelet is estimated, it is used to estimate seismic reflection coefficients in the seismic inversion. The distribution is a function of velocity and density changes in the.
Zero phase and minium phase wavelets have the same amplitude spectrum. Thus, information about the phase spectrum of the observed signal is lost or substantially distorted. This is the simplest method of zero phase conversion, often improves resolution and well ties and. An overview of wavelet transform concepts and applications. Phase and polarity assessment of seismic data seg wiki. I will illustrate how to obtain a good timefrequency analysis of a signal using the continuous wavelet transform. Synthetic ricker wavelets of 15, 30, 45, 60, 75, 90, 120, 150 and 180 degree phase are then generated. In such cases, it is necessary to convert the source wavelet into its minimum phase. First, there exists certain traditionalism in using seismic. The results are correlated with the pwave log curve. Non zero phase wavelets are converted to zero phase wavelets to achieve the best resolution of the seismic data. This research has identified various phenomena at or below tuning, but a consistent interpretation of thin beds is still a challenge and requires another approach. This assumption is used so that the wavelets autocorrelation can be derived from the seismic traces autocorrelation. Effect of seismic wavelet phase on post stack inversion.
The recent advances in the broadband seismic technologies offers the interpreter additional information in the form of high geologic resolution. Enlargement from corresponding parts in lower right of figures 7 and 8 showing significant improvements in the definition of faults are seen on the zero phase seismic data b. Resolution temporal resolution, principles of net thickness estimation, resolution. A onedimensional pulse, usually the basic response from a single reflector. The introduction of controlled phase acquisition and processing strategies has improved our control of seismic phase trantham, 1994. The zero phase wavelet and its phase spectrum were estimated from each of the deconvolved profile shown in figure 4. There are two special types of phase spectra of specific interest.
Since this optimization problem is nonlinear, the method is computationally. The minimum phase wavelet has a short time duration and a concentration of energy at the start of the wavelet. How do we convert the seismic trace wavelet to zero phase. The wavelet originates as a packet of energy from the. It is generally more compact than the equivalent minimum phase wavelet and is, overall, easier to interpret. Well, you can still estimate the phase spectrum of your wavelet directly from the seismic data by using the method velis and ulrych 1996 and optimized by misra and sacchi 2007 based on 4th order cumulant matching between the seismic trace and an allpass filter. Both are called zero phase wavelets and are a minimum delay. These reflection coefficients are then convolved with a suitable zero or minimum phase wavelet and choosing a frequency response similar to that of seismic. The appllcatlon of optimal wavelets in seismic inversion 19761. The mean mixed phase wavelet is then used to deconvolve the data.
Hilterman, 1985 tom wilson, department of geology and geography zero versus minimum hilterman, 1985. Its key attributes are its amplitude, frequency and phase. When the estimated constant phase of the statistical wavelet is consistent with the final result, the wavelet estimation converges more quickly than when starting with a zero phase. The limits of resolution of zero phase wavelets, geophysics, v. Vertical resolution seismic resolution is a measure of how large an object need to be in order to be seen in seismic. Mixedphase wavelet estimation a case study cseg recorder. The estimation of minimum phase wavelets from dynamite data and the estimation of zero phase wavelets from vibroseis generally use the assumption of a random reflectivity sequence. The influence of spatial sampling on resolution cseg. We know that achieving a zero phase wavelet is difficult, and thus it would be helpful if authors in this journal provide a comment on the phase of the data they are presenting in their interpretations. How do zero phase and minimum phase wavelets differ in. Seismic bandwidth, wavelet shape and descriptions of phase, zero phasing, enhancing frequency content, broadband vs conventional streamer.
From that we concluded that wavelets are powerful tools for analysis of field data, that is coming from analysis data and it is an excellent tool of field data compression. The damping parameter, c, controls the rate at which the timedomain wavelet, and frequency domain spectrum, is driven toward zero. Known zero phase well synthetics and vertical seismic profiles vsps can be compared with local surface seismic data to. Vertical and lateral seismic resolution and attenuation. Feb 26, 2018 zero phase and minium phase wavelets have the same amplitude spectrum. Resolving prospective pay zones through interpretation and.
Comparison of highresolution and conventionalresolution. The synthetic traces are produced by picking up the sonic and density logs for a well and calculating the reflection coefficients. Lateral resolution in seismic reflectiona physical model. Generally, wavelets are intentionally crafted to have specific properties that make them useful for signal processing. An ideal seismic source would be a spike maximum amplitude at every frequency, but the best practical one would be minimum phase. White and obrien 1974 discus sed this approach fmm a practical viewpoint. Zero offset vsp s providing precise velocity information, as well as true seismic wavelet welltie with phase, frequency, and timedepth, a zero offset vsp is the only tool that can identify. Reflections on the deconvolution of land seismic data cseg. Estimate a short conventional wavelet from a preferred workflow 2. Well, you can still estimate the phase spectrum of your wavelet directly from the seismic data by using the method velis and ulrych 1996 and optimized by misra and sacchi 2007 based on 4th order cumulant matching between the seismic. Reflections on the deconvolution of land seismic data. The wavelet originates as a packet of energy from the source point, having a specific origin in time, and is returned to the receivers as a series of events distributed in time and energy. Timevarying wavelet estimation and its applications in.
The author pointed out that the simulation result is close to measured result using zero phase ricker. That is, the maximum energy is at the beginning of the wavelet. Hentz, 2004, highfrequency sequence stratigraphy from seismic. Several windows can be extracted and results compared to synthetic seismograms for accuracy. Software a list of useful wavelet transform frameworks, libraries, and other software hazewinkel, michiel, ed. Thus, the high resolution process reveals prospective productive locations that are not apparent on a conventional seismic inversion. The desired output wavelet is designed to preserve the total energy of the farfield signature. Deconvolution during seismic processing can convert data of mixed phase to zero phase data, but is not always successful.
The most striking improvement seen in the zero phase seismic data figure 10b is the ability to define faults more accurately. An template of some rotated wavelets here would help with this. They observed that in the noisefree, zero phase case when at least two octaves of white bandwidth are present, the limit of temporal resolution. The autocorrelation process will always result in zerophase signal, and it does not depend on the inputs phase. Wavelets and deconvolution vertical seismic profile as a phase tool the fresnel zone improving spatial resolution improving resolution of depth estimation sample processing sequences ramifications of processing decisions noise. Therefore, the phase of the signal that is contained in matrix \\mathbfa\ in eq. Widess 6 observed that the composite wavelet within this zone basically retains its shape while its amplitude changes. If the source wavelet in the seismic trace is not minimum phase, the deconvolution produces unstable results.
However, although signal \a\left t \right\ resembles zero phase wavelet fig. Amplitude, frequency and bandwidth and their relationship. A novel seismic wavelet estimation method sciencedirect. The effect of low frequencies on seismic analysis provide more compact wavelets, better vertical resolution and definition of the parameters involved in deconvolution, and more realistic pseudosonic estimates.
According to dey 1999, the major wavelets in the real seismic data can be represented by zero phase ricker wavelets. Linear phase shift is described by a function that represents a line in the frequency domain. Quantifying resolution analytic spatial wavelets in a wellregarded empirical study, kallweit and wood 1982 used the rayleigh criterion described in figure 1 to quantify temporal resolution. The des ignature operator is obtained by matching the raw farfield signature to the desired zero phase wavelet. This is one reason why zero phase wavelets are usually output in seismic. Another goal of deconvolution is to produce a wavelet with a simple phase character, ideally a zero phase wavelet, which is the same for every trace in the seismic dataset.
The wavelet is symmetrical about the zero time and has energy at negative time. The mixed phase wavelet s beergut, which has grown with depth due to absorption. Seismic amplitude is an invaluable daytoday tool for graduate students and industry professionals in geology, geophysics, petrophysics, reservoir engineering, and all subsurface disciplines making regular use of seismic data. When tying, make a note of the phase disparity at the well many software tools let you plot correlation coefficient against phase rotation. A zero phase wavelet has a shorter duration than its minimum phase equivalent, which makes it a wavelet with higher resolving power. Preconditioning of seismic data prior to impedance inversion. An operator is then constructed which converts the minimum phase wavelet to the zero phase wavelet and this operator is then applied to the seismic data. Notice that the amplitude size of the side lobes is decreasing as well with increasing bandwidth. Hence data processing today makes every effort to deliver the data in a zero phase condition. The wavelet could also be extracted from the seismic.
To begin, let us load an earthquake signal in matlab. However, since all frequencies 565 hertz are zero phase, the seismic image provides an accurate representation of the geology. This attitude to the phase spectra of seismic signals can be explained by several facts. Hilterman, 1985 tom wilson, department of geology and geography zero. As time localization increases large c, frequency localization decreases, and vice versa. Seismic interpretation below tuning with multiattribute.
Pertaining to seismic data whose wavelet is symmetrical about zero time. A good workflow is to tie wells with a zero phase wavelet, at least at first. Preconditioning of seismic data prior to impedance inversion january 2016 satinder chopra ritesh kumar sharma the calibration of seismic data with the available well control is an important step that provides the link between seismic reflections, their stratigraphic interpretation and subsequent prediction of reservoir and fluid properties. Crains petrophysical handbook generating seismic wavelets. Apr 12, 2017 zeng 2015 showed with wedge models that a 90 phaserotated wavelet, similar to the hilbert transform, produces better definition of beds below tuning than zerophase wavelets. The phase is obtained by forcing a wellderived synthetic to match the seismic. Further, an average estimated mixed phase wavelet is obtained by taking the mean of the individual mixed phase wavelets. Understanding seismic detection and resolution of highfrequency sequences and systems tracts. A reflector with a graduated top may be a strong reflector on a conventional section and a weak reflector on a high resolution. Approximation of zero phasing if the interpreter does not have access to software for detailed wavelet shaping, an approximation to zero ohase can often be achieved by simple phase. This is then followed by zero or minimum phase wavelet estimation at the wells, where the reflectivity series is known both from the well as well as from the seismic. A zero at the zero frequency also means that the average value of the wavelet in the time domain must be zero.
Earth science stack exchange is a question and answer site for those interested in the geology, meteorology, oceanography, and environmental sciences. Deconvolution attempts to compress the wavelet, thereby increasing the resolution of the seismic data. Mixed phase wavelets distort the seismic image and can lead to incorrect interpretations. This filter is your mixed phase wavelet at that one well location. We examine field seismic data to test the benefits of 90 degrees phase wavelets in thinbed interpretation that are predicted by seismic modeling in part 1 of this paper. Understanding seismic detection and resolution of high. It can typically be visualized as a brief oscillation like one recorded by a seismograph or heart monitor. The phase is obtained by forcing a wellderived synthetic to match the seismic, thus assuming the well log provides ground truth. When tying, make a note of the phase disparity at the well many software tools let you plot correlation coefficient against phase. Well logs are often used for the estimation of seismic wavelets.
Estimate a broadband constant phase wavelet from the seismic. Zero phase data tend to provide sharper definition and less distortion between stratigraphic features in the subsurface, such as sand and shale layers. Resolution temporal resolution, principles of net thickness estimation, resolution vs detection sections and maps. The reflection time for a zero phase wavelet is at the central peak or trough, so picking reflection times is much easier and accurate for zero phase wavelets. Zero phase wavelets are symmetrical with the dominant loop corresponding to the reflection from the acoustic boundary. Physical seismic model experiments have been undertaken to study the detectability and lateral resolution of buried linear reflecting targets slits in an aluminium. If you do this at a couple wells and notice that the wavelet is relatively consistent, you can average the wavelets and apply the method of txpaulm to make your entire seismic data zero phase. Figure 3 shows that a zero phase wavelet comprises frequency components that have peaks aligned at zero time.
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