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SH-and SV-reflection waves after minimizing cross-component energy. Residual crosscomponents XY and YX after minimization are also shown. The E curve indicates the effectiveness of the minimization. High values of the SH-to SVwave energy ratio SH/SV indicate that the SH-reflection has been determined unambiguously. The dashed line in the SH-wave panel represents the S-wave reflection traveltime.
Source publication
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 aco...
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Context 1
... reflection data, after correction for tool rotation according to equation 9, are used in equation 13 to determine the strike of the reflector. The 4-C data following this procedure are shown in Figure 8 with the maximum-versus-minimum cross-energy relative difference E calculated from equation 15 and the SH-SV-wave energy ratio calculated from equation 17. The SH-and SV-reflection data computed from equations 16 are also displayed. ...
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... SH-wave reflection data in contrast to the alternating amplitudes of its xx and yy counterparts; see Figure 7 now shows continuous reflection events. After minimization according to equation 11, the XY and YX residuals Figure 8 show greatly reduced amplitudes compared to their counterparts before minimization Figure 7. Correspondingly, the E relative energy difference curve shows large values, indicating the minimization was effective. Figure 9 shows the final reflector image derived from the SHwave reflection data. ...
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... angle of the intersection of the reflectors with the borehole is less than 10° dip angle 80°, which means the wavepaths to and from the reflector are almost normal to the borehole. The near-normal radiation and reception direction correspond with the zones of near-zero amplitudes of the SV-wave radiation Figure 3 and reception Figure 2 patterns, which explains the lack of SV-reflections in the data Figure 8. ...
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... event intersects the borehole at an angle of about 6°, which agrees with observations from core samples Tang et al., 2009. Using this angle of intersection and the S-wave slowness profile of Figure 6, we computed the S-wave reflection traveltime and overlaid it on the processed SH-wave reflection data of Figure 8 see Tang et al. 2008 for the traveltime calculation. The S-wave traveltime tracks the reflection event from that depth very well and confirms that the reflection events of Figure 8 are reflected S-waves. ...
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... this angle of intersection and the S-wave slowness profile of Figure 6, we computed the S-wave reflection traveltime and overlaid it on the processed SH-wave reflection data of Figure 8 see Tang et al. 2008 for the traveltime calculation. The S-wave traveltime tracks the reflection event from that depth very well and confirms that the reflection events of Figure 8 are reflected S-waves. ...
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Citations
... Single-well reflection imaging can be classified as monopole reflected P-wave imaging and dipole reflected S-wave imaging (Hornby, 1989;Tang and Patterson, 2009). The reflected P-wave imaging logging technology using a monopole source was proposed by Hornby (1989). ...
Azimuthal acoustic reflection imaging logging, which can measure the distance and azimuth of geological bodies beside the borehole within a range of tens of meters, is becoming an important technology for geophysical applications. Measurements for single-well acoustic reflection imaging in the model with a 1:1 reflection interface outside the borehole provide physical validation of this technique. In this paper, the analytical solution for the monopole reflection wavefield in the fluid-filled borehole is deduced by using the virtual source analogy. The simulation shows that the radiation wave from the nearby borehole is equivalent to the reflected wave from the reflector outside the borehole. On this basis, the experimental idea of using two parallel wells to achieve the verification experiment of single-well azimuthal reflected P-wave imaging is proposed. The experimental results show that the amplitude and arrival time of the azimuthal reflected P wave are sensitive to the azimuth of the reflector outside the borehole. This information can be used for precise positioning of geological anomalies outside the borehole. Under the guidance of theoretical simulations and experiments, the prototype of azimuthal reflected P-wave imaging logging tool was designed independently. Field tests were conducted, recording high signal-to-noise ratio azimuthal reflected P wave.
... Following the monopole P-wave technology, Tang (2004) is the first to develop the theory and method of S-wave reflection imaging using the low-frequency dipole source, enabling azimuthal sensitivity and enhancing penetration depth for the imaging application. With many years of development and practice, dipole Swave reflection imaging is now a maturing technology in field applications (Tang and Patterson, 2009, Tang et al., 2014Lee et al., 2019;Xu et al., 2019). Nevertheless, it should be noted that a drawback of dipole S-wave imaging is the 180°ambiguity. ...
... For reflection imaging away from the borehole, the virtual source distance r 0 2 is many wavelengths away from the borehole, such that jη F v r 0 2 j ≫ 1. This allows us to accurately calculate the wavenumber integration of equation 17 using the steepest descent method (Tang and Patterson, 2009) as follows: ...
... For the dipole modeling in Figure 3c and 3d, the radial displacement is calculated by differentiating fluid pressure along the receiving direction for WL (for ALWD, the pressure difference of two receivers at the opposite sides of the collar is taken). The WL amplitude variation for the SH-wave incidence shows symmetric patterns at 90°and 270°, showing the typical 180°ambiguity of dipole measurement (Tang and Patterson, 2009). In contrast, the ALWD pattern shows strong azimuthal asymmetry. ...
Acoustic reflection imaging has been successfully applied in post-drilling wireline logging (WL), and the technique is potentially more valuable in acoustic logging while drilling (ALWD), particularly in geosteering while drilling. Because of the common occurrence of tool eccentering in drilling, the impact of drill collar eccentricity on the acoustic wavefield inside and outside the borehole must be considered. Therefore, we analyze the effect of an eccentric drill collar on acoustic reflection imaging while drilling using analytical solutions in a dual-cylindrical coordinate system. The virtual source analogy and the translational addition theorem for cylindrical Bessel functions are used to calculate the response of the fluid-filled borehole with an eccentric collar to the incident wavefield from a formation reflector. The analysis results are validated with those from 3D finite-difference simulations. We also studied the azimuthal variation of the received wavefield and compared the results with their centralized counterparts, for which the effects of collar eccentricity, frequency of the source, and formation elastic property are analyzed. The results show that the asymmetric feature of the wavefield due to the eccentric collar allows for determining the azimuth of the reflector, providing a solution to the azimuth ambiguity problem of borehole acoustic reflection imaging. Our results, besides developing an effective method for eccentric collar ALWD modeling, can be used to provide a theoretical foundation for ALWD tool development and data interpretation.
... For instance, parameters of acoustic velocities of seismic waves penetrated through the soil specimens can be used as a dataset for the estimation of soil strength in a laboratory using the reflectivity of P-waves [3,4]. Furthermore, data processing aimed to investigate the strength, elasticity, and mineral properties of soil specimens, which can can be performed using the acoustic imaging and seismic testing by measuring the velocities of P-and S-waves [5][6][7] as well as X-ray-diffraction (XRD) for testing the mineral content of soil [8]. ...
Evaluating the subground properties during the initial stage of a construction of building is important in order to estimate the suitability of soil quality to the technical requirements of bearing capacity, resistance to stress, and strength. This study presented the evaluation of the geotechnical properties of soil intended for the construction of Max IV facility of Lund University, performed in fieldwork and laboratory. The in situ methods included drilling boreholes, core sampling and assessment, crosshole measurements, and borehole logging. The laboratory-based measurements were performed at Swedish Geotechnical Institute and combined seismic measurements of drill cores, determination of the uniaxial compressive strength (UCS), and examination of material property: sieve analysis and natural moisture content. UCS was evaluated with regard to velocities of elastic P-waves. The synchronous light test by X-ray diffraction was performed for qualitative analysis of mineral composition of samples. The study applied integrated approach of the diverse geophysical methods to solve practical tasks on the evaluation of foundation strength and geotechnical parameters. This study demonstrated the benefits of integrated seismic and geophysical methods applied to soil exploration in civil engineering for testing quality of foundation materials.
... A monopole or dipole acoustic logging tool usually consists of a transmitting source and arrays of the hydrophones and can provide a 2D image (Tang & Patterson 2009), and the measurement results of the tool are underground information in the direction of the well axis and perpendicular to the well axis (Esmersoy et al. 1998;Haldorsen et al. 2010). This kind of logging tool has no azimuthal resolution and cannot accurately describe the downhole formation in 3D. ...
... The adaptive beamforming method using multidirectional array acoustic logging data was also proposed (Li & Yue 2015). Tang & Patterson (2009) used the cross dipole measurement to identify the direction of the reflector. The far-detecting acoustic logging based on cross dipole shear wave imaging was studied (Tang 2004;Tang & Cheng 2004;Wei et al. 2013;Tang et al. 2016;Li et al. 2022). ...
The performance of the azimuthal receiving piezoelectric vibrator has a major impact on the azimuthal acoustic logging tool. The evaluation of the performance and selective preference of piezoelectric vibrators through experimental methods will help improve the measurement accuracy of the tool. A heating tester was developed to test the static capacitance, resonant frequency, admittance and receiving amplitude of the vibrator at different temperatures. Far-field underwater acoustic tests were used to analyse the peak-to-peak amplitude, sensitivity and −3 dB angle of the vibrator and to determine the amplitude correction coefficients of each vibrator. The horizontal directivity of the azimuthally receiving phased subarray was also tested. Compared with the values at room temperature, the resonant frequency of the piezoelectric vibrator decreases by 9.20%, the static capacitance increases by 21.33% and the amplitude increases by 5.29% at a high temperature of 155°C. The underwater acoustic test showed that the main lobe of the receiving directional characteristic of the vibrator is symmetrical along the 0° main maximum direction, the −3 dB angle of the main lobe is 115°–142° and the average sensitivity level is −209.38 dB. The −3 dB angle of the receiving subarray is 66° and 60° without and with phase delay, respectively, and the energy of the received waveform is significantly increased. The piezoelectric vibrator can function stably at high temperatures, and its performance can be recovered after heating. It has good azimuthal resolution and high sensitivity, but the amplitude response has some discretion which needs to be corrected.
... The results can only judge the distance from the structure to the borehole and cannot explain its azimuth [19]. In order to overcome the shortcomings of the monopole P-wave method, Tang et al. introduced the dipole S-wave reflection acoustic logging technology, which used a dipole source and dipole receiver in reflection acoustic logging [20][21][22][23]. This method uses the orthogonal dipole source to radiate the shear wave to the formation outside the well and receives the shear wave reflected from the formation to image the structure near the borehole. ...
Reflection acoustic logging is a new technology for identifying geological structures around the well. It can be used to describe the geological structure, such as formation interface, fracture, and limestone cave. Based on the acoustic logging tool composed of the source and array receiver, the method can be used to image the geological structure around the well. Through migration imaging, the section crossing the well can be obtained in any azimuth. In the current three-dimensional (3D) display technology of reflection acoustic logging, the reflection plane around the well is always displayed as a reflection arc. The arc surface correction method can correct the arc surface in 3D imaging into a plane. According to the similarity criterion in a physical experiment and the need for practical research, we designed a scale model well experiment of dipole reflection acoustic logging. We obtained the 3D display of the reflection structure around the well by the experiment and realized the arc surface correction of the 3D display in reflection acoustic logging. The application shows the method can qualitatively describe the lateral extension length of the geological structure around the well. After the arc surface correction, the geological structure can be more accurately described.
... In order to detect 3D structural and compositional information around a well by logging 46 technique, it is necessary to predict the effect of complex structures on the acoustic logging data (Hornby, 1989;Tang, 2004;Tang and Patterson, 2009;Zhang and Hu, 2014;Xu et al., the simulation, it is necessary to define the relationship between the quality factor Q and 124 the viscoelastic parameters such as relaxation time. 125 According to the Boltzmann superposition principle, the relationship between the stress 126 and strain of a linear viscoelastic medium is defined as the convolution relationship in the 127 time domain, ...
In this paper, a model of the heterogeneous anelastic seismic wave problem is proposed in three-dimensional (3D) cylindrical coordinates. We use the velocity-stress formula to describe the realistic attenuation properties of viscoelastic materials, derived from a rheological model of the generalized standard linear solid (GSLS). The equation system is completed by additional equations for the anelastic functions including the strain history of the material. We apply the staggered grid finite-difference (FD) method in 3D cylindrical coordinates to solve the equations. Moreover, to avoid the effect of gradual expansion of the grid size as the radius increases, we use a variable grid method to achieve compensation. In real drilling operations, the mud injected in the borehole is a fluid with viscous properties. The actual formation is also not elastic. In the synthetic data of acoustic logging while drilling (LWD), we find that the drill collar wave is not affected by the viscoelastic parameters of the formation. In contrast, the Stoneley wave is more sensitive to the viscosity of the drilling fluid. The phase and amplitude of the received waveform are affected by the drilling fluid as well as the formation viscoelasticity. Therefore, the development of the cylindrical variable-grid FD method provides a flexible and efficient numerical technique to solve 3D viscoelastic wave propagation problems, including realistic attenuation and complex geometry.
... Early techniques primarily used P-waves from a monopole tool (Hornby, 1989;Fortin et al., 1991;Esmersoy et al., 1997). Later developments use S-waves from a dipole tool (Tang and Patterson, 2009;Bolshakov et al., 2011). A dipole source can radiate SV and SH types of shear waves into the formation. ...
... We now discuss the role of the orientation parameters and from the dipole S-wave imaging in the fracture stress analysis. The S-wave imaging uses acoustic data from a modern cross-dipole tool (for details, see Tang and Patterson, 2009). The imaging application obtains the fracture azimuth from the four-component (4C) data (xx, xy, yx, yy) of the tool using an azimuth rotation scheme, where the SH shear-wave data are constructed from the 4C data with a trial polarization angle (Tang and Patterson, 2009;Lee et al., 2019): ...
... The S-wave imaging uses acoustic data from a modern cross-dipole tool (for details, see Tang and Patterson, 2009). The imaging application obtains the fracture azimuth from the four-component (4C) data (xx, xy, yx, yy) of the tool using an azimuth rotation scheme, where the SH shear-wave data are constructed from the 4C data with a trial polarization angle (Tang and Patterson, 2009;Lee et al., 2019): ...
The assessment of fracture fluid-conducting capability in reservoirs is of great significance for hydrocarbon production, especially for tight reservoirs with fractures as the main reservoir fluid transport conduits. In recent years, dipole shear-wave reflection imaging technology has been effectively applied to identify near-well formation fractures and determine their orientation, but the evaluation of the fluid-conducting effectiveness of the acoustically imaged fractures remains a challenging task. To accomplish this task, this paper proposes a method that combines dipole acoustic reflection imaging with a geomechanical analysis to determine the stress state on the fracture surface. The fracture orientation and inclination, as obtained from the borehole reflection imaging, are combined with in-situ stress conditions to calculate the effective stress state of the fracture surface using a three-dimensional (3D) Mohr-diagram analysis, which, when compared with the Mohr-Coulomb failure criterion, determines whether the fracture is in the critically stressed state and is therefore fluid conductive. Most importantly, our analysis shows that the typical 180° fracture orientation azimuth uncertainty in the cross-dipole shear-wave imaging does not affect the determination of the stress state on the fracture surface in the Mohr-diagram analysis so that the two methods can be effectively combined to form a new method for evaluating the fluid-conducting effectiveness of fractures. The application examples from fractured reservoirs show the effectiveness of the new evaluation method, and the evaluation results can be used to provide useful information for field development and production planning.
... In recent years, dipole shear-wave imaging has made significant progress detecting geological structures outside the well, such as fractures, faults, and dissolution caves (Tang & Patterson 2009;Bradley et al. 2011;Tang et al. 2014;Patterson et al. 2016;Lee et al. 2019;Wang et al. 2020). It has also been used to delineate an existing open or cased borehole from a nearby well (Tang et al. 2016;Gu et al. 2021). ...
Radiation and reception responses of a dipole acoustic logging tool placed eccentrically in borehole fluid are an interesting and important topic in acoustic reflection imaging. Herein, we present a thorough research study on these responses. We treat the wave incidence from the reflector as the radiation from a virtual source and use the cylindrical-wave expansion method to solve both the wave radiation and reception problems for the off-centred tool, which, by using the steepest-descent method, yields asymptotic solutions for modelling the radiation and reception wavefeld characteristics. The modelling results from the analytical solution and the 3D finite-difference method were in good agreement. Specifcally, we analysed the radiation directivity of an eccentric dipole source in a fluid-flled borehole. The results revealed that the radiation pattern was asymmetric with respect to the borehole, and the asymmetry was determined by the eccentric distance, source frequency and formation properties. In particular, for the typical 3 kHz dipole logging frequency, the radiation was stronger in the off-centred direction than in the opposite direction. The asymmetry of the eccentric radiation resulted in a signifcant amplitude difference relative to its centred counterpart, which provided a potential method for addressing the 180° azimuth ambiguity of the dipole source. We used a theoretical waveform modelling example to demonstrate this advantage. Therefore, the results of this study provide a theoretical foundation for the development and application of dipole shear-wave imaging technology.
... To get over the disadvantages of monopole-source far detection logging, the dipole-source shear wave far detection logging technology was proposed. It has attracted much attention in practical application due to its deep radial detection depth, azimuth sensitivity, and fracture sensitivity [11][12][13]. In practice, the reflected shear waves are affected by the radiation of the dipole source in the ...
In shear wave far detection logging, dipole-source radiation is the main factor influencing the amplitude of the reflected shear waves. In this paper, a method is derived with the far-field asymptotic solution to calculate the dipole-source radiation of shear waves in a fluid-filled borehole. Then the dipole-source radiation of the shear waves is simulated under both low and high frequencies. In addition, the influences of formation elastic parameters on the dipole-source radiation of the shear waves are analyzed and the variations of the radiation characteristics of the shear wave with source main frequency and borehole radius are compared. Results show that the density and compressional wave velocity of the formation have little effect on the dipole-source radiation of the shear waves. However, the shear wave velocity not only affects the shear wave amplitude radiated to the formation by the dipole source (radiation performance), but also affects the energy distribution of the shear wave at different locations in space (radiation direction). The dipole source has better radiation performance and radiation coverage at low frequency and the optimal excitation frequency in different formations is very close, which is good for the application of this technology under different circumstances. At low frequency, the borehole has little influence on the dipole-source radiation, no matter how large the borehole radius is. However, at high frequency, the borehole modulation of the dipole-source radiation cannot be ignored, especially at large borehole radius.
... One is to use the P-P waves radiated from a monopole source and reflected back at the impedance interface outside of the borehole (Hornby, 1989;Wang et al., 2015;Hirabayashi et al., 2017;Bennett, 2019). The other is to use the S-S waves excited by a directional dipole source (Tang, 2004;Tang and Patterson, 2009). In recent years, both methods, especially the dipole S-wave method, have been applied in oil & gas exploration successfully. ...
In view of most wells are completed by casing pipe in oil & gas exploration and development process, it is imperative to extend the application of borehole acoustic reflection imaging (BARI) from open to cased boreholes. To understand the characteristics of signals in borehole acoustic imaging, we study the radiated and reflected elastic waves in an open and cased borehole through numerical simulations. The results show that, for a broadband dipole source, the radiated SH-waves have the highest amplitudes and broadest radiation angles in the cased borehole, which is similar to the observation in an open borehole. It is believed that the cement and casing pipe would prevent to a certain extent the energy excited by the inner borehole sources from propagating into the outside formation. However, our modeling results clearly show the existence of the cement and casing will not influence the amplitude of the radiated SH-waves significantly. In fact, the decrease of the borehole radius, which is caused by cased borehole completion here, will increase the amplitude of the radiated SH-waves. As a result, the signal-to-noise ratio (SNR) of reflected waves relative to direct waves in the cased borehole is higher than that in the open borehole. Meanwhile, the cement bond quality does not heavily affect the SNR of the reflected waves and the SNR increases with the decrease of source frequency. Interestingly, as the cutoff frequency of the dipole flexural-wave mode in the cased borehole increases rapidly with the decrease of the formation S-wave velocity, the amplitude of the direct wave also decreases significantly. This results in an increase of SNR of the reflected waves, which is beneficial for extracting the reflected waves. The field data example certifies our theoretical analysis. Our results provide a theoretical foundation for the through-casing BARI with a dipole source.
