A borehole-model-derived algorithm for estimating QP logs from full-waveform sonic logs

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. E107-E117 ◽  
Author(s):  
Jorge O. Parra ◽  
Pei-cheng Xu ◽  
Chris L. Hackert
Keyword(s):  
Spectral Ratio ◽  
Exact Formula ◽  
Seismic Attenuation ◽  
Absolute Difference ◽  
Head Wave ◽  
Full Waveform ◽  
Lower Accuracy ◽  
Head Waves ◽  
Geometric Spreading ◽  
Sonic Logs

We develop a processing algorithm to estimate the intrinsic seismic attenuation [Formula: see text] from P head waves of full-waveform sonic logs. The algorithm, based on an extended version of the amplitude spectral ratio (ASR) method, corrects the apparent attenuation for the effects of multiple raypaths within the borehole, geometric spreading of head waves, and formation inhomogeneity. The algorithm is derived from two ray models. The first model simulates the interaction among rays reflected within the borehole and rays reflected from layer interfaces. This model removes these reflections and extracts the leading borehole wavelet. The second model uses a single-ray model for the borehole head wave in layered formations. This model provides the transmission coefficients across the layer interfaces between the source depth and the receiver depth with sectional geometric spreading within these layers. We use these two models to simultaneously separate, correct for, and normalize the effects of the borehole, geometric spreading, and layering. Then we test the accuracy and limits of the models using the finite-difference solution of a point source in a fluid-filled borehole surrounded by uniform and layered formations. In 255 tested cases, the absolute difference between the estimated and exact divided by the exact [Formula: see text] is within 3% for more than half of the cases and 5% for more than two-thirds of the cases. The lower accuracy in the remaining cases is associated mainly with certain receiver locations with regard to the layer interfaces and is caused by the limitations of the ray models.

Polarization method for the determination of Poisson’s ratio in boreholes

Geophysics ◽  
1985 ◽  
Vol 50 (12) ◽  
pp. 2808-2816
Author(s):  
T. W. Spencer ◽  
Ru Chuan Wu
Keyword(s):  
Poisson’S Ratio ◽  
Shear Velocity ◽  
Poisson's Ratio ◽  
Head Wave ◽  
Velocity Measurements ◽  
Polarization Method ◽  
Full Waveform ◽  
Sensitive Function ◽  
Sonic Logs

Conventional methods for determining Poisson’s ratio from full‐waveform sonic logs rely on measurement of the shear velocity. This measurement is subject to significant error from contamination by events which do not travel at the shear velocity; it fails in soft formations where the shear head wave and pseudo‐Rayleigh waves are not excited. A new method is presented for determining Poisson’s ratio and shear velocity. This method can be implemented by recording the components of particle displacement on the borehole wall. The particle trajectory in the compressional head wave is rectilinear and is deflected with respect to the direction of propagation. The deflection is a sensitive function of Poisson’s ratio, varying by more than 30 degrees over the range of Poisson’s ratios encountered in rocks. In the polarization method all the measurements are made on the compressional head wave, the spatial resolution is greater than for velocity measurements, and the deflection is greatest in soft formations.

Numerical computation of individual far‐field arrivals excited by an acoustic source in a borehole

Geophysics ◽  
1985 ◽  
Vol 50 (5) ◽  
pp. 852-866 ◽  
Author(s):  
Andrew L. Kurkjian
Keyword(s):  
Numerical Computation ◽  
The Body ◽  
Body Waves ◽  
Head Wave ◽  
Far Field ◽  
Trapped Mode ◽  
Full Waveform ◽  
Full Wave ◽  
Head Waves ◽  
Strong Shear

In this paper, I model the acoustic logging problem and numerically compute individual arrivals at far‐field receivers. The ability to compute individual arrivals is useful for examining the sensitivities of each arrival to various factors of interest, as opposed to examining the full waveform as a whole. While the numerical computation of the mode arrivals (Peterson, 1974) and the numerical computation of the first head waves (Tsang and Rader, 1979) have been previously reported, the numerical computation of the entire set of head‐wave arrivals is new and is the major contribution of this paper. Following Roever et al. (1974) and others, the full wave field is represented as a sum of contributions from both poles and branchcuts in the complex wavenumber plane. The pole contributions correspond to mode arrivals while the branch cuts are associated with the body waves (i.e., head waves). Both the pole and branch cut contributions are computed numerically and results are presented for the cases of a slow and a fast formation. The shear event in the slow formation is found to be relatively small, consistent with observations in measured data. Contrary to existing knowledge, the shear event in the fast formation is also relatively small. The apparent strong shear arrival in the full waveforms is due primarily to the trapped mode pole in the vicinity of cutoff.

Least‐squares inversion of in‐situ sonic Q measurements: Stability and resolution

Geophysics ◽  
2004 ◽  
Vol 69 (2) ◽  
pp. 378-385 ◽  
Author(s):  
Aristotelis Dasios ◽  
Clive McCann ◽  
Timothy Astin
Keyword(s):  
High Resolution ◽  
Least Squares ◽  
Instantaneous Frequency ◽  
Spectral Ratio ◽  
Full Waveform ◽  
Multiple Measurements ◽  
Sandstone Reservoir ◽  
Gas Bearing

We minimize the effect of noise and increase both the reliability and the resolution of attenuation estimates obtained from multireceiver full‐waveform sonics. Multiple measurements of effective attenuation were generated from full‐waveform sonic data recorded by an eight‐receiver sonic tool in a gas‐bearing sandstone reservoir using two independent techniques: the logarithmic spectral ratio (LSR) and the instantaneous frequency (IF) method. After rejecting unstable estimates [receiver separation <2 ft (0.61 m)], least‐squares inversion was used to combine the multiple estimates into high‐resolution attenuation logs. The procedure was applied to raw attenuation data obtained with both the LSR and IF methods, and the resulting logs showed that the attenuation estimates obtained for the maximum receiver separation of 3.5 ft (1.07 m) provide a smoothed approximation of the high‐resolution measurements. The approximation is better for the IF method, with the normalized crosscorrelation factor between the low‐ and high‐resolution logs being 0.90 for the IF method and 0.88 for the LSR method.

A STUDY OF TWO‐DIMENSIONAL HEAD WAVES IN FLUID AND SOLID SYSTEMS

Geophysics ◽  
1963 ◽  
Vol 28 (4) ◽  
pp. 563-581 ◽  
Author(s):  
John W. Dunkin
Keyword(s):  
Half Space ◽  
Vertical Displacement ◽  
Point Of View ◽  
Head Wave ◽  
Apparent Velocity ◽  
Two Dimensional ◽  
Multiple Reflections ◽  
Transient Wave ◽  
Line Load ◽  
Head Waves

The problem of transient wave propagation in a three‐layered, fluid or solid half‐plane is investigated with the point of view of determining the effect of refracting bed thickness on the character of the two‐dimensional head wave. The “ray‐theory” technique is used to obtain exact expressions for the vertical displacement at the surface caused by an impulsive line load. The impulsive solutions are convolved with a time function having the shape of one cycle of a sinusoid. The multiple reflections in the refracting bed are found to affect the head wave significantly. For thin refracting beds in the fluid half‐space the character of the head wave can be completely altered by the strong multiple reflections. In the solid half‐space the weaker multiple reflections affect both the rate of decay of the amplitude of the head wave with distance and the apparent velocity of the head wave by changing its shape. A comparison is made of the results for the solid half‐space with previously published results of model experiments.

Q estimation from vertical seismic profile data and anomalous variations in the central North Sea

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 615-626 ◽  
Author(s):  
S. D. Stainsby ◽  
M. H. Worthington
Keyword(s):  
North Sea ◽  
Pulse Width ◽  
Spectral Ratio ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Recording Equipment ◽  
Vertical Seismic Profile ◽  
High Attenuation ◽  
Vsp Data ◽  
Central North Sea

Four different methods of estimating Q from vertical seismic profile (VSP) data based on measurements of spectral ratios, pulse amplitude, pulse width, and zeroth lag autocorrelation of the attenuated impulse are described. The last procedure is referred to as the pulse‐power method. Practical problems concerning nonlinearity in the estimating procedures, uncertainties in the gain setting of the recording equipment, and the influence of structure are considered in detail. VSP data recorded in a well in the central North Sea were processed to obtain estimates of seismic attenuation. These data revealed a zone of high attenuation from approximately 4 900 ft to [Formula: see text] ft with a value of [Formula: see text] Results of the spectral‐ratio analysis show that the data conform to a linear constant Q model. In addition, since the pulse‐width measurement is dependent upon the dispersive model adopted, it is shown that a nondispersive model cannot possibly provide a match to the real data. No unambiguous evidence is presented that explains the cause of this low Q zone. However, it is tentatively concluded that the seismic attenuation may be associated with the degree of compaction of the sediments and the presence of deabsorbed gases.

Dynamic properties of reflected and head waves near the critical point

1979 ◽  
Vol 16 (7) ◽  
pp. 1388-1401 ◽  
Author(s):  
Larry W. Marks ◽  
F. Hron
Keyword(s):  
Exact Solution ◽  
High Frequency ◽  
Classical Problem ◽  
Plane Boundary ◽  
Head Wave ◽  
Disk File ◽  
Ray Theory ◽  
Computational Point ◽  
Spherical Waves ◽  
Head Waves

The classical problem of the incidence of spherical waves on a plane boundary has been reformulated from the computational point of view by providing a high frequency approximation to the exact solution applicable to any seismic body wave, regardless of the number of conversions or reflections from the bottoming interface. In our final expressions the ray amplitude of the interference reflected-head wave is cast in terms of a Weber function, the numerical values of which can be conveniently stored on a computer disk file and retrieved via direct access during an actual run. Our formulation also accounts for the increase of energy carried by multiple head waves arising during multiple reflections of the reflected wave from the bottoming interface. In this form our high frequency expression for the ray amplitude of the interference reflected-head wave can represent a complementary technique to asymptotic ray theory in the vicinity of critical regions where the latter cannot be used. Since numerical tests indicate that our method produces results very close to those obtained by the numerical integration of the exact solution, its combination with asymptotic ray theory yields a powerful technique for the speedy computation of synthetic seismograms for plane homogeneous layers.

Exact seismograms for a point force using generalized ray theory

Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1421-1427 ◽  
Author(s):  
E. R. Kanasewich ◽  
P. G. Kelamis ◽  
F. Abramovici
Keyword(s):  
Half Space ◽  
Near Field ◽  
Sedimentary Basins ◽  
Transverse Component ◽  
Point Force ◽  
Seismic Exploration ◽  
Head Wave ◽  
Vertical Force ◽  
Low Velocity ◽  
Head Waves

Exact synthetic seismograms are obtained for a simple layered elastic half‐space due to a buried point force and a point torque. Two models, similar to those encountered in seismic exploration of sedimentary basins, are examined in detail. The seismograms are complete to any specified time and make use of a Cagniard‐Pekeris method and a decomposition into generalized rays. The weathered layer is modeled as a thin low‐velocity layer over a half‐space. For a horizontal force in an arbitrary direction, the transverse component, in the near‐field, shows detectable first arrivals traveling with a compressional wave velocity. The radial and vertical components, at all distances, show a surface head wave (sP*) which is not generated when the source is compressive. A buried vertical force produces the same surface head wave prominently on the radial component. An example is given for a simple “Alberta” model as an aid to the interpretation of wide angle seismic reflections and head waves.

scholarly journals Microseismic hydraulic fracture imaging in the Marcellus Shale using head waves

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. KS1-KS10 ◽  
Author(s):  
Zhishuai Zhang ◽  
James W. Rector ◽  
Michael J. Nava
Keyword(s):  
Marcellus Shale ◽  
P Wave ◽  
Head Wave ◽  
Wave Polarization ◽  
Horizontal Section ◽  
Location Accuracy ◽  
Arrival Times ◽  
Microseismic Data ◽  
Head Waves ◽  
Event Location

We have studied microseismic data acquired from a geophone array deployed in the horizontal section of a well drilled in the Marcellus Shale near Susquehanna County, Pennsylvania. Head waves were used to improve event location accuracy as a substitution for the traditional P-wave polarization method. We identified that resonances due to poor geophone-to-borehole coupling hinder arrival-time picking and contaminate the microseismic data spectrum. The traditional method had substantially greater uncertainty in our data due to the large uncertainty in P-wave polarization direction estimation. We also identified the existence of prominent head waves in some of the data. These head waves are refractions from the interface between the Marcellus Shale and the underlying Onondaga Formation. The source location accuracy of the microseismic events can be significantly improved by using the P-, S-wave direct arrival times and the head wave arrival times. Based on the improvement, we have developed a new acquisition geometry and strategy that uses head waves to improve event location accuracy and reduce acquisition cost in situations such as the one encountered in our study.

Experiments and Computations for KCS Added Resistance for Variable Heading

2015 ◽  
Author(s):  
Hamid Sadat-Hosseini ◽  
Serge Toxopeus ◽  
Dong Hwan Kim ◽  
Teresa Castiglione ◽  
Yugo Sanada ◽  
...  
Keyword(s):  
Surface Profile ◽  
Engine Performance ◽  
Head Wave ◽  
Added Resistance ◽  
Local Flow ◽  
Wake Field ◽  
Head Waves ◽  
Calm Water ◽  
Free Surface Profile ◽  
Peak Location

Experiments, CFD and PF studies are performed for the KCS containership advancing at Froude number 0.26 in calm water and regular waves. The validation studies are conducted for variable wavelength and wave headings with wave slope of H/λ=1/60. CFD computations are conducted using two solvers CFDShip-Iowa and STAR-CCM+. PF studies are conducted using FATIMA. For CFD computations, calm water and head wave simulations are performed by towing the ship fixed in surge, sway, roll and yaw, but free to heave and pitch. For variable wave heading simulations, the roll motion is also free. For PF, the ship model moves at a given speed and the oscillations around 6DOF motions are computed for variable wave heading while the surge motion for head waves is restrained by adding a very large surge damping. For calm water, computations showed E&lt;4%D for the resistance,&lt;8%D for the sinkage, and &lt;40%D for the trim. In head waves with variable wavelength, the errors for first harmonic variables for CFD and PF computations were small, &lt;5%DR for amplitudes and &lt;4%2π for phases. The errors for zeroth harmonics of motions and added resistance were large. For the added resistance, the largest error was for the peak location at λ/L=1.15 where the data also show large scatter. For variable wave heading at λ/L=1.0, the errors for first harmonic amplitudes were &lt;17%DR for CFD and &lt;26%DR for PF. The comparison errors for first harmonic phases were E&lt;24%2π. The errors for the zeroth harmonic of motions and added resistance were again large. PF studies for variable wave headings were also conducted for more wavelength condition, showing good predictions for the heave and pitch motions for all cases while the surge and roll motions and added resistance were often not well predicted. Local flow studies were conducted for λ/L=1.37 to investigate the free surface profile and wake field predicted by CFD. The results showed a significant fluctuation in the wake field which can affect the propeller/engine performance. Additionally it was found that the average propeller inflow to the propeller is significantly higher in waves.

Évaluation du facteur de qualité sismique au barrage de Carillon (Québec)

2001 ◽  
Vol 28 (3) ◽  
pp. 496-508
Author(s):  
B Giroux ◽  
M Chouteau ◽  
L Laverdure
Keyword(s):  
Survey Design ◽  
Spectral Ratio ◽  
Microseismic Monitoring ◽  
Seismic Attenuation ◽  
P Wave ◽  
Q Value ◽  
A Value ◽  
P Wave Velocity ◽  
Aggregate Composition

The seismic attenuation in concrete has seldom been studied, although it is an important parameter for survey design. In this paper, the seismic Q factor is estimated from data measured at the Carillon dam. Three methods were used for this study: amplitude decay yielding a value of 5.1 ± 1.6, spectral ratio giving a value of 8.3 ± 3.5, and a value of 7.5 ± 14.9 was obtained from the rise-time technique. These values are weak compared with what is generally observed in rocks, and slightly lower than values obtained on laboratory concrete samples. However, the average P wave velocity measured on the investigated area is 4081 ± 95 m·s–1, an indication of the good quality of the material. Consequently, this strong attenuation could be attributed on one hand to energy loss, and on the other hand to scattering caused by the intrinsic cement–aggregate composition of concrete. It is also possible that an inadequate sensor coupling had the effect of reducing the observed Q value. Key words: seismic attenuation, concrete dams, microseismic monitoring, coupling.

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