Mapping formation radial shear‐velocity variation by a constrained inversion of borehole flexural‐wave dispersion data

2010 ◽  
Author(s):  
X. M. Tang ◽  
D. Patterson
Keyword(s):  
Shear Velocity ◽  
Wave Dispersion ◽  
Velocity Variation ◽  
Flexural Wave ◽  
Dispersion Data

Mapping formation radial shear-wave velocity variation by a constrained inversion of borehole flexural-wave dispersion data

Geophysics ◽  
2010 ◽  
Vol 75 (6) ◽  
pp. E183-E190 ◽  
Author(s):  
Xiao-Ming Tang ◽  
Douglas J. Patterson
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
High Frequency ◽  
Wave Dispersion ◽  
Velocity Variation ◽  
Flexural Wave ◽  
Inversion Method ◽  
Dispersion Characteristics ◽  
Dispersion Data

We have developed a novel constrained inversion method for estimating a radial shear-wave velocity profile away from the wellbore using dipole acoustic logging data and have analyzed the effect of the radial velocity changes on dipole-flexural-wave dispersion characteristics. The inversion of the dispersion data to estimate the radial changes is inherently a nonunique problem because changing the degree of variation or the radial size of the variation zone can produce similar wave-dispersion characteristics. Nonuniqueness can be solved by developing a constrained inversion method. This is done by constraining the high-frequency portion of the model dispersion curve with another curve calculated using the near-borehole velocity. The constraint condition is based on the physical principle that a high-frequency dipole wave has a shallow penetration depth and is therefore sensitive to the near-borehole shear-wave velocity. We have validated the result of the constrained inversion with synthetic data testing. Combining the new inversion method with four-component crossed-dipole anisotropy processing obtains shear radial profiles in fast and slow shear polarization directions. In a sandstone formation, the fast and slow shear-wave profiles show substantial differences caused by the near-borehole stress field, demonstrating the ability of the technique to obtain radial and azimuthal geomechanical property changes near the wellbore.

Mapping formation shear-velocity variation by inverting logging-while-drilling quadrupole-wave dispersion data

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D491-D498 ◽  
Author(s):  
Yuan-Da Su ◽  
Xiao-Ming Tang ◽  
Chun-Xi Zhuang ◽  
Song Xu ◽  
Long Zhao
Keyword(s):  
Velocity Profile ◽  
High Frequency ◽  
Shear Velocity ◽  
Wave Dispersion ◽  
Physical Principle ◽  
Equivalent Model ◽  
Velocity Variation ◽  
Inversion Method ◽  
Dispersion Data ◽  
Logging While Drilling

The logging-while-drilling (LWD) quadrupole wave is a dispersive wave mode guided along the borehole with a drill collar. The wave is sensitive to the formation alteration caused by drilling. We inverted LWD quadrupole-wave dispersion data to estimate a radial shear-velocity profile away from the wellbore. We also explored the nonuniqueness of the inverse problem and solved it by using a constrained inversion method. This was done by constraining the high-frequency portion of the model dispersion curve with another curve calculated using the near-borehole velocity. The constraint condition is based on the physical principle that a high-frequency LWD quadrupole wave has a shallow penetration depth and is therefore sensitive to the near-borehole shear velocity. Particularly, we found that a monotonically continuous velocity profile can be well approximated using a one-zone equivalent model, allowing for a drastic simplification of the inversion process. We used theoretical modeling and real data examples to validate the method for the LWD wave data. The quadrupole dispersion data and the inversion results clearly demonstrated that formation alteration can occur even while the well is being drilled.

Model-based dispersive processing of borehole dipole wave data using an equivalent-tool theory

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. D35-D43 ◽  
Author(s):  
Sheng-Qing Lee ◽  
Xiao-Ming Tang ◽  
Yuan-da Su ◽  
Chun-Xi Zhuang
Keyword(s):  
Data Processing ◽  
Dispersion Curve ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Flexural Wave ◽  
Dispersion Characteristics ◽  
Acoustic Data ◽  
Model Based ◽  
Dispersion Data ◽  
Application Procedure

We have developed a model-based processing technique for borehole dipole S-wave logging data to estimate formation shear slowness from the data. During dipole acoustic logging, the presence of the logging tool can significantly affect the dispersion characteristics of flexural waves. Therefore, modeling the effects of the tool is essential for model-based processing. We have determined that an equivalent-tool theory using only two parameters, tool radius, and modulus, can adequately model the flexural-wave-dispersion characteristics. We used this theory, together with a calibration procedure, to determine the tool parameters to formulate an inversion method for the logging data processing. Our use of the equivalent tool theory played an important role in fitting the theoretical dispersion curve to the actual flexural-wave-dispersion data, enabling fast processing of the field acoustic data. An advantage of this model-based method is its prediction power, which, in the absence of low-frequency dispersion data, allows for predicting formation shear slowness from the low-frequency limit of the model-fitted dispersion curve. We have also developed an application procedure of the method for field-data processing and demonstrated its effectiveness in the dispersion correction using field acoustic data from fast and slow formations.

Determining formation S-wave transverse isotropy from borehole flexural-wave dispersion data

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. D47-D55 ◽  
Author(s):  
Song Xu ◽  
Xiao-Ming Tang ◽  
Yuan-Da Su ◽  
Sheng-Qing Lee ◽  
Chun-Xi Zhuang
Keyword(s):  
Transverse Isotropy ◽  
Transversely Isotropic ◽  
Wave Dispersion ◽  
Flexural Wave ◽  
Stoneley Wave ◽  
S Wave ◽  
Acoustic Logging ◽  
Wave Measurements ◽  
Dispersion Data ◽  
Ti Media

Many earth formations are characterized as transversely isotropic (TI) media. In acoustic logging through a vertical borehole, the S-wave TI property has traditionally been determined from borehole monopole Stoneley-wave measurements, but the feasibility of shear-TI estimation from dipole flexural waves has not been fully investigated. We have developed a methodology to determine the TI parameters from borehole dipole-flexural wave data. Our analysis shows that the Stoneley wave is sensitive to the TI property mainly in an acoustically slow formation, and the sensitivity diminishes when the formation becomes faster. The advantage of the flexural wave over the Stoneley wave is that the former wave is sensitive to the TI property in the slow and fast formations, provided the wave measurement is made in a broad frequency range in which the flexural-wave dispersion characteristics from low to high frequencies can be used. By calculating the theoretical flexural-wave dispersion curve for the TI formation and using it to fit the measured wave dispersion data, we can simultaneously determine the vertical and horizontal S-wave velocities, from which the S-wave TI parameter is obtained. Application of our methodology to field data processing shows that the TI parameter estimated from the flexural wave is almost identical to that from the Stoneley wave for a slow formation. For a fast formation, the flexural-wave result is more accurate and reliable compared with the Stoneley-wave result. Our study, thus, introduces a novel application of dipole acoustic logging.

scholarly journals Anomalous azimuthal variations with 360° periodicity of Rayleigh phase velocities observed in Scandinavia

2020 ◽  
Vol 224 (3) ◽  
pp. 1684-1704
Author(s):  
Alexandra Mauerberger ◽  
Valérie Maupin ◽  
Ólafur Gudmundsson ◽  
Frederik Tilmann
Keyword(s):  
Seismic Anisotropy ◽  
Broad Band ◽  
Shear Velocity ◽  
Velocity Variation ◽  
The South ◽  
Study Region ◽  
Lithospheric Thickness ◽  
Phase Velocities ◽  
The North ◽  
Southern Norway

SUMMARY We use the recently deployed ScanArray network of broad-band stations covering most of Norway and Sweden as well as parts of Finland to analyse the propagation of Rayleigh waves in Scandinavia. Applying an array beamforming technique to teleseismic records from ScanArray and permanent stations in the study region, in total 159 stations with a typical station distance of about 70 km, we obtain phase velocities for three subregions, which collectively cover most of Scandinavia (excluding southern Norway). The average phase dispersion curves are similar for all three subregions. They resemble the dispersion previously observed for the South Baltic craton and are about 1 per cent slower than the North Baltic shield phase velocities for periods between 40 and 80 s. However, a remarkable sin(1θ) phase velocity variation with azimuth is observed for periods >35 s with a 5 per cent deviation between the maximum and minimum velocities, more than the overall lateral variation in average velocity. Such a variation, which is incompatible with seismic anisotropy, occurs in northern Scandinavia and southern Norway/Sweden but not in the central study area. The maximum and minimum velocities were measured for backazimuths of 120° and 300°, respectively. These directions are perpendicular to a step in the lithosphere–asthenosphere boundary (LAB) inferred by previous studies in southern Norway/Sweden, suggesting a relation to large lithospheric heterogeneity. In order to test this hypothesis, we carried out 2-D full-waveform modeling of Rayleigh wave propagation in synthetic models which incorporate a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup reproduces the observations qualitatively, and results in higher phase velocities for propagation in the direction of shallowing LAB, and lower ones for propagation in the direction of deepening LAB, probably due to the interference of forward scattered and reflected surface wave energy with the fundamental mode. Therefore, the reduction in lithospheric thickness towards southern Norway in the south, and towards the Atlantic ocean in the north provide a plausible explanation for the observed azimuthal variations.

scholarly journals Crustal Velocity Models Retrieved from Surface Wave Dispersion Data for Gujarat Region, Western Peninsular India

2019 ◽  
Vol 23 (2) ◽  
pp. 147-155
Author(s):  
Vishwa Joshi
Keyword(s):  
Wave Dispersion ◽  
Data File ◽  
Western India ◽  
Nonlinear Inversion ◽  
S Wave ◽  
Surface Wave Dispersion ◽  
Peninsular India ◽  
Velocity Models ◽  
Crustal Velocity ◽  
Dispersion Data

The physiographic features of Gujarat state of western India are unique, as they behaved dynamically with several alterations and modifications throughout the geological timescale. It displays a remarkable example of a terrain bestowed with geological, physiographical and climatic diversities. The massive 2001 Bhuj earthquake (M 7.7) over the Kachchh region caused severe damage and devastation to the state of Gujarat and attracted the scientific community of the world to comprehend on its structure and tectonics for future hazard reduction. In the present study, three clusters of wave paths A, B1, and B2 have considered. In each cluster, dispersion data were measured station by station which collectively formed a dispersion data file for a nonlinear inversion through Genetic algorithm. In this way, three crustal velocity models were generated for entire Gujarat. These models are 1) Across Cambay Basin (Path A), 2) Along Saurashtra - Kathiawar Horst (Path B1) and 3) Along Narmada Basin (Path B2), which were formed at different times during the Mesozoic. The average thickness of the crust estimated in the present study for paths A, B1 and B2 are 38.2 km, 36.2 km, and 41.6 km respectively and the estimated S-wave velocity in the lower crust is ~ 3.9 km/s for all the paths. The present study will improve our knowledge about the structure of the seismogenic layer of this active intraplate region 

scholarly journals Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952*

1954 ◽  
Vol 44 (3) ◽  
pp. 471-479
Author(s):  
Maurice Ewing ◽  
Frank Press
Keyword(s):  
Internal Friction ◽  
Rayleigh Waves ◽  
Shear Velocity ◽  
Velocity Curve ◽  
The Core ◽  
Long Period ◽  
A Value ◽  
The Earth ◽  
Dispersion Data ◽  
Kamchatka Earthquake

Abstract Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952, are analyzed. The new Palisades long-period vertical seismograph recorded orders R6–R15, the corresponding paths involving up to seven complete passages around the earth. The dispersion data for periods below 400 sec. are in excellent agreement with earlier results and can be explained in terms of the known increase of shear velocity with depth in the mantle. Data for periods 400-480 sec. indicate a tendency for the group velocity curve to level off, suggesting that these long waves are influenced by a low or vanishing shear velocity in the core. Deduction of internal friction in the mantle from wave absorption gives a value 1/Q = 370 × 10−5 for periods 250-350 sec. This is a little over half the value reported earlier for periods 140-215 sec.

scholarly journals Higher mode surface waves and their bearing on the structure of the earth's mantle

1964 ◽  
Vol 54 (1) ◽  
pp. 161-182
Author(s):  
Robert L. Kovach ◽  
Don L. Anderson
Keyword(s):  
Group Velocity Dispersion ◽  
Shear Velocity ◽  
Wave Dispersion ◽  
Abrupt Increase ◽  
Low Velocity ◽  
Surface Wave Dispersion ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Mode Group ◽  
Velocity Zone

abstract A detailed numerical investigation of surface wave dispersion and particle motion associated with the higher Love and Rayleigh modes over realistic earth models has been carried out as a preliminary to the routine use of these waves in studies of the crust-mantle system. The suggestion that the so-called channel waves, such as the Lg, Li, and Sa phases, can be interpreted by higher mode group velocity dispersion curves is verified in detail. Furthermore, Sa should have a higher velocity across shield areas than across normal continental areas and a higher velocity across continents than across oceans. Higher mode Rayleigh wave data are presented for long oceanic paths to Pasadena. The observed data favor the CIT 11 model of Anderson and Toksöz (1963) over the 8099 model of Dorman et al. (1960) and indicate that under the Pacific Ocean the low-velocity zone extends to a depth perhaps as deep as 400 km followed by an abrupt increase in shear velocity.

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