Delineating a cased borehole in unconsolidated formations using dipole acoustic data from a nearby well

Geophysics ◽  
2021 ◽  
pp. 1-39
Author(s):  
Gu Xihao ◽  
Xiao-Ming Tang ◽  
Yuan-Da Su
Keyword(s):  
Shear Waves ◽  
Low Frequency ◽  
Well Being ◽  
Compressional Wave ◽  
Acoustic Imaging ◽  
Wave Radiation ◽  
Dipole Source ◽  
Compressional Waves ◽  
Single Well ◽  
Cased Borehole

A potential application for single-well acoustic imaging is the detection of an existing cased borehole in the vicinity of the well being drilled, which is important for drilling toward (when drilling a relief well), or away from (collision prevention), the existing borehole. To fulfill this application in the unconsolidated formation of shallow sediments, we propose a detection method using the low-frequency compressional waves from dipole acoustic logging. For this application, we perform theoretical analyses on elastic wave scattering from the cased borehole and derive the analytical expressions for the scattered wavefield for the incidence of compressional and shear waves from a borehole dipole source. The analytical solution, in conjunction with the elastic reciprocity theorem, provides a fast algorithm for modeling the whole process of wave radiation, scattering, and reception for the borehole acoustic detection problem. The analytical results agree well with those from 3D finite-difference simulations. The results show that compressional waves, instead of shear waves as commonly used for dipole acoustic imaging, are particularly advantageous for the borehole detection in the unconsolidated formation. Field data examples are used to demonstrate the application in a shallow marine environment, where dipole-compressional wave data in the measurement well successfully delineate a nearby cased borehole, validating our analysis results and application.

Imaging near‐borehole structure using directional acoustic‐wave measurement

Geophysics ◽  
2004 ◽  
Vol 69 (6) ◽  
pp. 1378-1386 ◽  
Author(s):  
Xiaoming M. Tang
Keyword(s):  
Low Frequency ◽  
Compressional Wave ◽  
Dipole Source ◽  
Measurement Tool ◽  
Data Set ◽  
Compressional Waves ◽  
Wave Measurement ◽  
Radial Extent ◽  
Multiple Component ◽  
Tool Rotation

This study shows how to image the structure of a near‐borehole geologic formation and determine its orientation using a directional acoustic measurement tool in the borehole. The advantage of the directional tool over a conventional monopole tool is that the former uses a dipole source and/or receiver to obtain multiple component data that are sensitive to the orientation of the structure. To preserve the orientation information in the presence of tool rotation, the multiple component data are converted from the tool‐frame coordinates into a fixed coordinate system using the recorded tool azimuth. The component data in the fixed coordinates are then used to image the formation structure and determine its orientation. The application of the method and procedure is demonstrated with a four‐component cross‐dipole data set measured in a deviated borehole. Using the directionality of the compressional waves in the dipole data, the method successfully obtains the orientation of bed boundaries crossing the borehole. In addition, the low‐frequency content (about 2–3 kHz) of the data allows for imaging the radial extent of the formation structure up to 15 m, greatly enhancing the penetration depth as compared to that obtained using conventional monopole compressional‐wave data.

Single-well S-wave imaging using multicomponent dipole acoustic-log data

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCA211-WCA223 ◽  
Author(s):  
Xiao-Ming Tang ◽  
Douglas J. Patterson
Keyword(s):  
Field Data ◽  
Wave Radiation ◽  
Dipole Source ◽  
Directional Sensitivity ◽  
S Wave ◽  
Fracture Characterization ◽  
Processing Application ◽  
S Waves ◽  
Wave Imaging ◽  
Single Well

Single-well S-wave imaging has several attractive features because of its directional sensitivity and usefulness for fracture characterization. To provide a method for single-well acoustic imaging, we analyzed the effects of wave radiation, reflection, and borehole acoustic response on S-wave reflection measurements from a multicomponent dipole acoustic tool. A study of S-wave radiation from a dipole source and the wave’s reflection from a formation boundary shows that the S-waves generated by a dipole source in a borehole have a wide radiation pattern that allows imaging of reflectors at various dip angles crossing the borehole. More importantly, the azimuthal variation of the S-waves, in connection with the multicomponent nature of a cross-dipole tool, can determine the strike of the reflector. We used our theoretical foundation for borehole S-wave imaging to formulate an inversion procedure for field data processing. Application to field data validates the theoretical results and demonstrates the advantages of S-wave imaging. Application to near-borehole fracture imaging clearly demonstrates S-wave azimuthal sensitivity to fracture orientation.

Sonic to ultrasonic Q of sandstones and limestones: Laboratory measurements at in situ pressures

Geophysics ◽  
2009 ◽  
Vol 74 (2) ◽  
pp. WA93-WA101 ◽  
Author(s):  
Clive McCann ◽  
Jeremy Sothcott
Keyword(s):  
Wave Attenuation ◽  
Shear Waves ◽  
Compressional Wave ◽  
Ultrasonic Frequency ◽  
Laboratory Measurements ◽  
Compressional Waves ◽  
Wave Velocities ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Laboratory measurements of the attenuation and velocity dispersion of compressional and shear waves at appropriate frequencies, pressures, and temperatures can aid interpretation of seismic and well-log surveys as well as indicate absorption mechanisms in rocks. Construction and calibration of resonant-bar equipment was used to measure velocities and attenuations of standing shear and extensional waves in copper-jacketed right cylinders of rocks ([Formula: see text] in length, [Formula: see text] in diameter) in the sonic frequency range and at differential pressures up to [Formula: see text]. We also measured ultrasonic velocities and attenuations of compressional and shear waves in [Formula: see text]-diameter samples of the rocks at identical pressures. Extensional-mode velocities determined from the resonant bar are systematically too low, yielding unreliable Poisson’s ratios. Poisson’s ratios determined from the ultrasonic data are frequency corrected and used to calculate thesonic-frequency compressional-wave velocities and attenuations from the shear- and extensional-mode data. We calculate the bulk-modulus loss. The accuracies of attenuation data (expressed as [Formula: see text], where [Formula: see text] is the quality factor) are [Formula: see text] for compressional and shear waves at ultrasonic frequency, [Formula: see text] for shear waves, and [Formula: see text] for compressional waves at sonic frequency. Example sonic-frequency data show that the energy absorption in a limestone is small ([Formula: see text] greater than 200 and stress independent) and is primarily due to poroelasticity, whereas that in the two sandstones is variable in magnitude ([Formula: see text] ranges from less than 50 to greater than 300, at reservoir pressures) and arises from a combination of poroelasticity and viscoelasticity. A graph of compressional-wave attenuation versus compressional-wave velocity at reservoir pressures differentiates high-permeability ([Formula: see text], [Formula: see text]) brine-saturated sandstones from low-permeability ([Formula: see text], [Formula: see text]) sandstones and shales.

Borehole coupling at sonic frequencies

Geophysics ◽  
1990 ◽  
Vol 55 (7) ◽  
pp. 806-814 ◽  
Author(s):  
J. R. Lovell ◽  
B. E. Hornby
Keyword(s):  
High Frequency ◽  
Incident Angle ◽  
Low Frequency ◽  
Compressional Wave ◽  
Elastic Plane ◽  
Coupling Term ◽  
Hankel Functions ◽  
Analytic Expressions ◽  
Single Well ◽  
Seismic Frequencies

An elastic plane wave incident on a borehole couples through the borehole wall to produce a compressional wave inside the borehole, and the effect of this coupling varies with incident angle. Imaging experiments that include a downhole source and/or hydrophones must account for this effect to achieve optimal results. In configurations pertinent to VSP surveys and cross‐well surveys at seismic frequencies, a low‐frequency source can be assumed. Recently, however, both cross‐well and single‐well imaging experiments have been undertaken at sonic frequencies (above 2000 Hz) where low‐frequency approximations are no longer valid. We have developed new formulas which are valid over all frequencies and incident angles. For both shear and compressional incident waves, we present explicit formulas to describe this dependence. Contrary to what might be expected from low‐frequency approximations, we find that at certain angles and for high enough frequencies, marked resonances in the coupling terms for both shear and compressional incidence occur. Moreover, at all frequencies, the borehole coupling term depends significantly upon incident angle. For a given incident angle, and for high enough frequencies, the coupling term becomes periodic in frequency. We give analytic expressions for these high‐frequency resonances and present a simplified high‐frequency approximation that can be computed without using Bessel or Hankel functions. Results are presented for three different formation types; very hard, medium hard, and soft. For all formation types, significant variations in amplitude as well as strong shifts in phase are apparent, as functions of both frequency and incident angle. This distortion of the wave field should be taken into account for any imaging experiment that uses high‐frequency signals.

Numerical simulation of radiation, reflection, and reception of elastic waves from a borehole dipole source

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. D253-D261 ◽  
Author(s):  
Zhou-Tuo Wei ◽  
Xiao-Ming Tang
Keyword(s):  
Numerical Simulation ◽  
Elastic Waves ◽  
Compressional Wave ◽  
Acoustic Imaging ◽  
P Wave ◽  
Dipole Source ◽  
Imaging Technology ◽  
Reflected Waves ◽  
Dipole System ◽  
Reflection Imaging

A recent advance in single-well reflection imaging is the use of a dipole acoustic system in a borehole to radiate and receive elastic waves to and from a remote geologic reflector in formation. This dipole-acoustic imaging technology is evaluated by numerically simulating the radiation and reflection of the wavefield generated by the borehole dipole source and analyzing the receiving sensitivity of the dipole system to the incoming reflected waves. The analyses show that a borehole dipole source can radiate a compressional wave (P-wave) and two types of shear waves (i.e., SV- and SH-waves) into the formation. The SH-wave has wide radiation coverage and the best receiving sensitivity, and is most suitable for dipole-shear imaging. In an acoustically slow formation, the dipole-generated P-wave has strong receiving sensitivity and can also be used for reflection imaging. An important feature of dipole imaging is its sensitivity to reflector azimuth, which results from the directivity of the dipole source. By using a 4C data acquisition method to record the dipole-generated reflected signal, the reflector azimuth can be determined. The numerical simulation and theoretical analysis results are in good agreement, providing a solid foundation for the dipole acoustic imaging technology.

Acoustic radiation and reflection of a logging-while-drilling dipole source

2019 ◽  
Vol 219 (1) ◽  
pp. 108-128 ◽  
Author(s):  
Zhoutuo Wei ◽  
Xiaoming Tang ◽  
Jingji Cao
Keyword(s):  
Frequency Band ◽  
Wave Reflection ◽  
Excitation Frequency ◽  
Radiation Efficiency ◽  
Wave Radiation ◽  
Dipole Source ◽  
Sh Wave ◽  
S Wave ◽  
Single Well ◽  
Logging While Drilling

SUMMARY With the comparison to the resistivity ultra-deep measurement, the single-well reflection survey in acoustic logging-while-drilling (ALWD) measurement lags far behind, especially ALWD dipole measurement has long been thought to be little added value. In this paper, we extended the dipole shear-wave (S-wave) reflection survey technology in wireline logging into ALWD and demonstrated the theoretical feasibility of adopting a dipole source–receiver system to perform ALWD reflection survey. For this purpose, we investigated the radiation patterns of radiantSH, SV and P waves, the energy fluxes of guided and radiant waves and their acoustical radiation efficiencies from an LWD dipole acoustic source by comparisons with the wireline results. The analysis results reveal that a dominant excitation-frequency band does exist in ALWD dipole S-wave reflection. Consequently, the expected excitation frequency should be located in the band of the signal with high radiation efficiency, guaranteeing the best radiation performance. In fast formations, SH wave is the best candidate for ALWD reflection survey due to its highest radiation efficiency. In contrast, the dominant excitation-frequency band of SH wave gets wider in a slow formation. Besides, the SV- and P-wave radiation efficiencies are also remarkable, implying that both waves can also be used for ALWD reflection survey in slow formations. We expounded the SH-, SV- and P-reflection behaviours at three typical excitation frequencies by our 3-D finite difference. Simulations to single-well reflection validate the key role of dominant excitation-frequency band and demonstrate the theoretical feasibility of applying the technology to ALWD. Our results can guide the design and measurement methods of ALWD dipole S-wave reflection survey tool, which could have extensive application prospect for geo-steering.

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

2012 ◽  
Vol 217-219 ◽  
pp. 2590-2593 ◽  
Author(s):  
Yu Wang ◽  
Bai Zhou Li
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Low Frequency ◽  
Dipole Source ◽  
Fluctuating Pressure ◽  
Common Structure ◽  
Hydrodynamic Noise ◽  
Near Field Sound ◽  
Equivalent Sources ◽  
Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

Foreshock wave transmission into the magnetosheath and magnetosphere: results from global hybrid-Vlasov simulations

2021 ◽  
Author(s):  
Lucile Turc ◽  
Markus Battarbee ◽  
Urs Ganse ◽  
Andreas Johlander ◽  
Yann Pfau-Kempf ◽  
...  
Keyword(s):  
Solar Wind ◽  
Mach Number ◽  
Cone Angle ◽  
Low Frequency ◽  
Compressional Wave ◽  
Wave Transmission ◽  
Wave Power ◽  
Solar Wind Flow ◽  
Magnetic Pulsations ◽  
Wave Properties

<p>The foreshock, extending upstream of the quasi-parallel shock and populated with shock-reflected particles, is home to intense wave activity in the ultra-low frequency range.<em> </em>The most commonly observed of these waves are the “30 s” waves, fast magnetosonic waves propagating sunward in the plasma rest frame, but carried earthward by the faster solar wind flow. These waves are thought to be the main source of Pc3 magnetic pulsations (10 – 45 s) in the dayside magnetosphere. A handful of case studies with suitable spacecraft conjunctions have allowed simultaneous investigations of the wave properties in different geophysical regions, but the global picture of the wave transmission from the foreshock through the magnetosheath into the magnetosphere is still not known. In this work, we use global simulations performed with the hybrid-Vlasov model Vlasiator to study the Pc3 wave properties in the foreshock, magnetosheath and magnetosphere for different solar wind conditions. We find that in all three regions the wave power peaks at higher frequencies when the interplanetary magnetic field strength is larger, consistent with previous studies. While the transverse wave power decreases with decreasing Alfvén Mach number in the foreshock, the compressional wave power shows little variation. In contrast, in the magnetosheath and the magnetosphere, the compressional wave power decreases with decreasing Mach number. Inside the magnetosphere, the distribution of wave power varies with the IMF cone angle. We discuss the implications of these results for the propagation of foreshock waves across the different geophysical regions, and in particular their transmission through the bow shock.</p>

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