Peak Frequency Method Research Articles

Investigation of formation and ultrasonic disassembling of RBC Aggregation aimed for maintenance of blood channel

AbstractEstablishment of real‐time monitoring technique for blood viscosity during extracorporeal circulation treatment is needed. We have demonstrated that red blood cell (RBC, hereafter) aggregation degree, which highly correlates with the blood viscosity, can be estimated by the ultrasound spectroscopic observation of the RBC and the defining of the peak frequency by the Fast Fourier Transform process. In this study, the peak frequency was measured to investigate the aggregation degree of RBC flowing in a simple heart‐lung machine. In addition, to disassemble the RBC aggregations that might cause the clogging of the circuit, a disassemble technique of the RBC aggregations using a focused 5 MHz ultrasonic transducer was also proposed. As the first step of this study, the disassembling of the RBC aggregations was carried out under the still condition and its effect was confirmed by the peak frequency method.

Bridge Inspection and Defect Recognition with Using Impact Echo Data, Probability, and Naive Bayes Classifiers

Interpretation of IE data have been carried out by analyzing IE signals in frequency domain to determine the maximum frequency. However, the current peak frequency method can be inaccurate. The purpose of this research is to introduce features in IE signals that can be used for effective classification and interpretation for bridge deck evaluation through statistical analysis and Naive Bayes classifiers. The dataset contained IE data collected from eight slabs created at Advanced Sensing Technology FAST NDE laboratory (FHWA). A set of statistical features in time domain, normalized peak values, and length of preprocessed signals were used to classify the IE data, statistically. Then, Naive Bayes classifiers was employed to recognize defect area. Finally, the result of statistical classification was compared with frequency approach. The result shows that 19 and 21% of the IE signals collected from the defect area have multiple peaks, respectively. However, 85% of the IE signals collected from the sound set had only one peak. A probability classifier was used to find the relationship between the result of the frequency method and statistical analysis. The result shows that 10% of the IE signals were usable for estimating the thickness in the sound group.

Seismic time–frequency analysis as a robust method to estimate the fluid saturation: A case study of carbonates reservoir, Iran

ABSTRACTThe propagation of seismic waves through a saturated reservoir compresses the fluid in the pore spaces. During this transition, parts of seismic energy would be attenuated because of intrinsic absorption. Rock physics models make the bridge between the seismic properties and petrophysical reality in the earth. Attenuation is one of the significant seismic attributes used to describe the fluid behaviour in the reservoirs. We examined the core samples using ultrasonic experiments at the reservoir conditions. Given the rock properties of the carbonate reservoir and experiment results, the patchy saturation mechanism was solved for substituted fluid using the theory of modulus frequency. The extracted relationship between the seismic attenuation and water saturation was used in time–frequency analysis. We performed the peak frequency method to estimate the Q factor in the Gabor domain and determined the water saturation based on the computed rock physics model. The results showed how the probable fault in the reservoir has stopped the fluid movement in the reservoir and caused touching the water‐bearing zone through drilling.

Estimation of the quality factor based on the microseismicity recordings from Northern Poland

We use the peak frequency method to estimate effective P- and S-wave quality factors (QP and QS) based on the recorded waveforms of microseismic events. We analyze downhole datasets recorded during the hydraulic stimulation of the two unconventional gas reservoirs located in the northern part of Poland. The effective attenuation is lower in the deeper reservoir consistent with higher compaction. In both cases, we observe high QS values relative to QP which is consistent with attenuation coefficients of saturated reservoirs.

Passive seismic measurement of seismic attenuation in Delaware Basin

Local earthquake activity can be employed to measure attenuation (the effective quality factor [Q]) and characterize production in the Delaware Basin, Texas, USA. To illustrate this, we employed data from the recently installed Texas Seismic Network (TexNet) seismic stations collected in the west Texas area between April 2017 and March 2018. Earthquake activity in the Delaware Basin has increased in comparison to the previous 20 years, which has resulted in numerous high-quality events suitable for this analysis. The high signal-to-noise ratio events were used to estimate effective Q factors using the peak frequency method on the sediments of the Delaware Basin. The effective attenuation of the sedimentary basin is 90 for P-waves and 140 for S-waves (both with uncertainty of approximately 30), indicating an unusually low attenuation (high Q) for S-waves relative to the P-waves. This is consistent with attenuation of a saturated sedimentary basin because the saturation results in less attenuation of S-waves. Additionally, we observe an increase of the effective Q factor with distance between the station and events consistent with rays sampling the deeper, less-attenuating, and less-saturated portions of the basin and even basement. Inverted effective attenuation coefficients were used to calculate moment magnitudes, which were consistent with those seen in the TexNet array.

Variations of attenuation and VP/VS ratio in the vicinity of wastewater injection: A case study of Costa Molina 2 well (High Agri Valley, Italy)

By analyzing seismicity induced by the injection of wastewater into the Costa Molina 2 well, we characterized attenuation in the area. Attenuation quality factors [Formula: see text] and [Formula: see text] were calculated using the peak-frequency method, which is suitable for small-magnitude earthquakes registered in the region. Anomalously high attenuation with values of effective [Formula: see text] and [Formula: see text] ratio of less than 1 in the vicinity of the injection well was found, in comparison with [Formula: see text] for the rest of the region. Furthermore, the [Formula: see text] ratio was also found to be high in the close vicinity of the injection well. We determine how sedimentary rocks possibly change their geomechanical properties due to salt-water injection and find that observed changes of attenuation (increase) and [Formula: see text] ratio (increase) are consistent with the geomechanical models and experiments. Our findings indicate that the observed anomaly in the vicinity of the Costa Molina 2 well is due to the (1) changes of the properties of the rock mass affected by injection and (2) 3D structure in the overburden rocks.

Applications of high-resolution time-frequency transforms to attenuation estimation

Attenuation estimates quantify the loss of energy of propagating seismic waves due to anelastic processes. It is often carried out in the frequency domain. The most well-known methods for attenuation estimation, such as the spectral ratio and frequency-shift methods, compare spectral shapes of waveforms along a given raypath. They require broad spectra such as those obtained with the Fourier transform and the continuous wavelet transform. These methods are incompatible with high-resolution time-frequency transforms, which drastically localize time-frequency information. On the other hand, these transforms indicate stronger resistance to noise and can be used in combination with the peak frequency method to estimate attenuation. We have applied high-resolution transforms, namely the synchrosqueezing transform, basis pursuit, and complete ensemble empirical-mode decomposition, to a synthetic wedge example and two seismic data set examples, a seismic reflection profile, and a vertical seismic profile (VSP). Results for the synthetic example find that most high-resolution transforms are able to reliably estimate quality factors. Using centroid frequencies, the seismic reflection profile exhibits local increases in centroid frequencies, which likely indicates imprints from apparent attenuation over intrinsic attenuation. Centroid frequencies and effective quality factors for the VSP are consistent for the different spectral estimation techniques. These three examples illustrate the value of high-resolution transforms for frequency and quality factor measurements.

THE VELOCITY DISPERSION AND ATTENUATION OF MARINE HYDRATE‐BEARING SEDIMENTS

AbstractP‐wave and S‐wave velocity will increase and the attenuation will vary when the concentration of gas hydrate increases. The analysis of velocity dispersion and attenuation for hydrate‐bearing sediments (GHBS) would contribute to the estimate of gas hydrate concentration. Based on effective medium theory (EMT), we study the nonlinear variation feature of P‐wave and S‐wave velocity for marine unconsolidated hydrate‐bearing sediments. Moreover, we use BISQ model to replace Gassmann equation in the EMT, and research the velocity dispersion and attenuation of hydrate‐bearing sediments in the full frequency band. Based on this model, the velocity and attenuation always increase with the increasing amount of gas hydrate, and the rock porosity and clay content doesn't make any differences to the attenuation. After the numeral modeling, we apply the sonic logging (20 kHz) and VSP (100 Hz) data from Ocean drilling Program (ODP) leg 164 in obtaining the concentration of gas hydrate stability zone (GHSZ). In the application, the average hydrate concentration of GHSZ from site 995 in ODP leg 164 is about 5%∼7%, and corresponds to the pressure core sample (PCS) data, Helgerud et al.'s research conclusions and the prediction data from neural network (NN). Due to the velocity dispersion, the estimated hydrate concentration from VSP data would be lower than the estimated results from sonic logging data. The prediction results of three hydrate Sites (SH2, SH3 and SH7) from Shenhu area also coincide with the PCS, South China Sea. Moreover, based on the peak frequency method, the effective seismic quality factors (Q) of the BSR are estimated from the inline prestack seismic gathers. The Q‐values suggest that the effective saturation of gas hydrate estimated by this model fluctuates between 15%∼30%. The results of numeral modeling and applications indicate the velocity dispersion and attenuation of GHBS always vary with the concentration of hydrate. The study of velocity dispersion and attenuation feature for GHBS in the full frequency band would contribute to the estimate of gas hydrate concentration.

Attenuation estimation using high resolution time–frequency transforms

Wave attenuation is often measured using spectral techniques such as the spectral ratio method and the frequency shift method, comparing the spectral content of pairs of waveforms along the ray path. The recent introduction of novel highly-localized time–frequency transforms leads to high-resolution but discontinuous spectra. It prevents the use of these time–frequency transforms with conventional attenuation measurement methods. We show how three highly-localized time–frequency transforms, namely basis pursuit, the synchrosqueezing wavelet transform, and complete ensemble empirical mode decomposition, can still be used to estimate attenuation using the peak frequency method. Assuming a Ricker source wavelet, the decrease in peak frequency of a wave spectrum as it propagates in a given medium is used to estimate attenuation. When applied to a synthetic benchmarking signal corrupted by Gaussian white noise, the three transforms show different degrees of performance and robustness for different signal-to-noise ratios. The developed methodology is suitable for geophysical investigations, but may also find application in other fields such as biomedicine, acoustics and engineering.

Attenuation from microseismic datasets by the peak frequency method benchmarked with the spectral ratio method

Recently proposed peak-frequency method is used to estimate the P- and S-wave quality factors from microseismic events. We use a downhole monitoring dataset of 10 high signal-to-noise ratio microseismic events to calculate P- and S-wave effective attenuation of a carbonate reservoir. We benchmark these results with the spectral ratio method and obtain mutually consistent results. Additionally we develop and test two techniques of peak frequency determination. We show that the peak frequency method can be successfully used in the estimation of the quality factor and it provides precise measurements of attenuation.

Source reverberations, near-surface resonances, or Q? Comment on “The peak frequency of direct waves for microseismic events” (Leo Eisner, Davide Gei, Miroslav Hallo, Ivo Opršal, and Mohammed Y. Ali, Geophysics, 78, no. 6, A45–A49)

In a recent Geophysics Letter, Eisner et al. (2013) measure peak frequencies in velocity spectra of direct waves from microseismic events. The authors interpret these peak frequencies as being caused by attenuation and use them for estimating the effective Q -factor of the medium. Nevertheless, I point out a significant problem with these results, namely, that the authors’ model for the earthquake source is not accurate enough to allow the determination of Q for the surrounding medium. This can be seen by considering the following question: Do the Q values reported in Eisner et al. (2013) characterize the medium, the source model, or the spectral data for direct arrivals? Eisner et al. (2013) assume the first of these answers to be correct; however, careful analysis shows that the correct answer is actually the last one. In answering the above question, note that the Q and t * values measured by this method are not unique physical properties of the medium because they change whenever a different source model is used. The flat plateau at f f c in the Eisner et al. (2013) source spectrum is unrealistic, and yet this plateau is the principal tool of the authors’ method for Q estimation. If we use, for example, Brune’s (1970) model as a more accurate one, then the Q would be much larger than the values reported by Eisner et al. (2013) (see the subsection “Meaning of Q ” below). Thus, the inferred Q s follow from the assumed source model. However, these Q values still cannot be viewed as corrections to the source model because even after these corrections, the model fits the observations very poorly (see the subsection “Data fit”). Therefore, the Q values proposed by Eisner et al. (2013) can only be interpreted as the observed spectral-peak frequencies heuristically multiplied by traveltimes: …

Estimation of seismic attenuation of gas hydrate bearing sediments from multi-channel seismic data: A case study from Krishna–Godavari offshore basin

Seismic attenuation of gas hydrate bearing sediments is estimated from the multi-channel seismic data acquired in Krishna–Godavari (KG) offshore basin in the vicinity of Site NGHP-01-10, where ∼128 m of fracture-filled hydrate is confirmed by drilling/coring, to understand the effect of gas hydrate on the seismic attenuation. The seismic quality factor (Q), which is the inverse of seismic attenuation, is estimated from two methods – first, the spectral ratio method which utilizes the logarithmic ratio of the seafloor and bottom simulating reflector (BSR) spectra; and second, the peak frequency method which depends upon the variations of the peak frequency of the BSR spectrum as a function of traveltime. In the study area, the complex fault system has perturbed the seafloor resulting in noisy seafloor spectrum. As a result, the logarithm of the spectral ratio was also noisy and the Q-values obtained from spectral ratio method were found to be unstable. On the other hand, the peak frequency method is found to be relatively stable as it depends only on the peak frequency of the BSR which can be reliably obtained by conventional processing. This method yields an effective Q value of BSR which represents a weighted average of the interval Q-values of the water column and the gas hydrate bearing sediments. Since the Q-value of water column can be treated as a constant, the variations in effective Q-value can be interpreted in terms of the variations of Q in the gas hydrate bearing sediments for a constant thickness of water column.The estimated effective Q-values, along the inline and crossline seismic profiles, depend on several factors such as gas hydrate, free gas and the complex fault system. The combined interpretation of the quality factor and the interval velocity model helps to understand these effects in different zones of the seismic data. The attenuation of the background marine sediments is estimated from the analysis of crossline seismic profile. The gas hydrate bearing sediments, as inferred from the velocity model, show low attenuation as compared to that of the background sediments. In contrast, active migration of free gas across the fault system leads to increase in seismic attenuation within the gas hydrate stability zone. The complex fault zone may also lead to an increase in seismic attenuation. The blanked seismic zone shows a marginal decrease in seismic attenuation probably related to load-bearing form of gas hydrate. Our attenuation results are compared against the results obtained from waveform inversion, albeit with a higher resolution. The relative variation of Q estimated from the proposed method is close to the average Q-values estimated from full waveform inversion for most of the CDPs. The proposed methodology can be a useful technique to estimate seismic attenuation from multi-channel seismic data.