Acoustic fields for monopole logging while drilling with an eccentric collar

Geophysics ◽  
2020 ◽  
pp. 1-144
Author(s):  
Yunjia Ji ◽  
Xiao He ◽  
Hao Chen ◽  
Xiuming Wang ◽  
Hailan Zhang
Keyword(s):  
Dispersion Analysis ◽  
Summation Method ◽  
Joint Analysis ◽  
Stoneley Wave ◽  
Branch Points ◽  
Head Waves ◽  
Logging While Drilling ◽  
Acoustic Responses ◽  
Full Waveforms ◽  
Acquisition Method

The acoustic problem of an eccentric drill collar in a fluid-filled borehole has been of interest in the field of acoustic logging while drilling (ALWD) in recent years. To reduce the effects of tool eccentricity on ALWD measurements, studies on acoustic responses under such conditions are essential. This study therefore has developed an analytical method to investigate borehole wavefields with an off-center monopole ALWD tool in both fast and slow formations. By evaluating the contributions of compressional and shear branch points, the effects of the tool eccentricity on individual formation primary and shear head waves were investigated. Results illustrate that tool eccentricity only affects the excitation properties, while it has almost no effect on the extracted velocities. The joint analysis of synthetic full waveforms and dispersion diagrams with varying eccentricity degrees indicates that multipole modes are excited when the tool is off-center, and their excitation amplitudes gradually increase with increasing eccentricity, especially in the direction of tool movement. Moreover, the dispersion analysis reveals that the two modes with intersections in the centered case are coupled when the tool becomes eccentric. In particular, the coupling performance between the Stoneley and flexural modes is the most prominent. Furthermore, the effects of tool eccentricity on the monopole acquisition method, i.e., the sum of waveforms received at four orthogonal azimuths, are evaluated. Results show that the above summation method can effectively reduce the effects of slight or moderate eccentricity. However, for large or extreme eccentricity, reducing or eliminating the effects of eccentricity on the Stoneley wave is a challenge for this method. Based on the above analyses, measurements may not be reliable for formation evaluation in the case of extreme eccentricity, especially for Stoneley wave applications.

scholarly journals The effects of tool eccentricity on individual P and S head waves in monopole acoustic LWD

2021 ◽  
Vol 18 (1) ◽  
pp. 74-84
Author(s):  
Yunjia Ji ◽  
Xiao He ◽  
Hao Chen ◽  
Xiuming Wang
Keyword(s):  
P Wave ◽  
Branch Points ◽  
Wave Excitation ◽  
Integration Technique ◽  
S Wave ◽  
Excitation Spectra ◽  
Low Frequencies ◽  
S Waves ◽  
Head Waves ◽  
Logging While Drilling

Abstract Velocities of P and S waves are main goals of downhole acoustic logging. In this work, we study the effects of an off-center acoustic tool on formation P and S head waves in monopole logging while drilling (LWD), which will be helpful for accurate interpretation of recorded logs. We first develop an analytic method to solve the wavefields of this asymmetric LWD model. Then using a branch-cut integration technique, we evaluate the contributions of branch points associated with P and S waves, and further investigate the effects of tool eccentricity on their characteristics of excitation, attenuation and waveforms. The analyses reveal that the variation of the excitation and attenuation of both P and S head waves with eccentricity depends on frequencies and receiver azimuths strongly. Besides, new resonance peaks appear in excitation spectra due to influences of poles of multipole modes near branch points when the monopole tool is off-center. According to semblance results of individual compressional and shear waveforms, extracted velocities are not affected by tool eccentricity in both fast and slow formations. In fast formations, spectra analyses indicate that S-wave excitation is more sensitive to tool eccentricity than P-wave. Moreover, resonance peaks in P-wave excitation spectra increase with the increasing eccentricity in all directions. In slow formations, off-center tools almost have no influence on both P and S waves at low frequencies, which suggests that the effects of tool eccentricity can be reduced by adjusting the source's operating frequency.

scholarly journals Electromagnetic propagation logging while drilling data acquisition method based on undersampling technology

2021 ◽  
Vol 18 (5) ◽  
pp. 653-663
Author(s):  
Xinghan Li ◽  
Wenxiu Zhang ◽  
Wenxuan Chen ◽  
Yali Zhang ◽  
Jian Zheng ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Correction Coefficient ◽  
Sampled Data ◽  
Electromagnetic Propagation ◽  
Oil And Gas Exploration ◽  
Unconventional Oil And Gas ◽  
Logging While Drilling ◽  
Analogue To Digital ◽  
Acquisition Method ◽  
Selection Of

Abstract With the development of complex and unconventional reservoirs, oil and gas exploration becomes increasingly difficult. Highly deviated wells/horizontal wells are widely used. The electromagnetic propagation logging while drilling (LWD) is more effective in complex geological environment detection owing to geological orientation and real-time formation evaluation. However, its operating frequency is generally at the MHz level. Traditional acquisition techniques require an analogue to digital converter with high sampling rates, which will introduce complex circuit structures and increase sampling costs. The undersampling technology has overcome these disadvantages. The difficulties in the undersampling technology include the selection of an undersampling frequency and the acquisition of a signal correction coefficient. The range of undersampling frequencies and a correction coefficient has been developed to process the electromagnetic propagation LWD measurements in this paper. The range of undersampling frequency ensures the validity of the sampled data. The correction coefficient ensures that different frequency signals use the same undersampling frequency to obtain the same frequency recovery signal. The correctness of these parameters is verified by simulation and field data examples. The range of undersampling frequency and a correction coefficient has been applied, improving the data stability and providing reliable technical support for the exploration and development of unconventional oil and gas.

scholarly journals Finite‐difference synthetic acoustic logs

Geophysics ◽  
1985 ◽  
Vol 50 (10) ◽  
pp. 1588-1609 ◽  
Author(s):  
R. A. Stephen ◽  
F. Cardo‐Casas ◽  
C. H. Cheng
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Two Dimensions ◽  
Body Waves ◽  
Head Wave ◽  
Stoneley Wave ◽  
Sharp Interface Model ◽  
Head Waves ◽  
The Finite Difference Method

The finite‐difference method is a powerful technique for studying the propagation of elastic waves in boreholes. Even for the simple case of an open borehole with vertical homogeneity, the snapshot format of the method displays clearly the interaction between the borehole and the rock, and the origin and evolution of phases. We present an outline of the finite‐difference method applied to the acoustic logging problem, including a boundary condition formulation for liquid‐solid cylindrical interfaces which is correct to second order in the space increments. Absorbing boundaries based on the formulations of Reynolds (1978) and Clayton and Engquist (1977) were used to reduce reflections from the grid boundaries. Results for a vertically homogeneous sharp interface model are compared with the discrete‐wavenumber method and excellent agreement is obtained. The technique is also demonstrated by considering sharp and continuous transitions (damaged zones) at the borehole wall and by considering the effects of washouts and horizontal fissures on acoustic logs. The latter two cases are examples of wave propagation in media with properties which vary in two dimensions. For the models considered, amplitudes of head waves and head wave multiples (leaky PL modes) are frequently enhanced by washouts. The compressional body waves are less affected by the washouts and horizontal fissures than the guided Stoneley waves which are reflected and only partially transmitted at changes in borehole radius. Amplitude changes of up to 6 dB are observed in the compressional wave due to the borehole deformation. For the Stoneley wave, borehole deformations can cause changes in amplitude of 20 dB and dramatic changes in waveform.

Complex roots of the Stoneley-wave equation

1972 ◽  
Vol 62 (1) ◽  
pp. 285-299
Author(s):  
Walter L. Pilant
Keyword(s):  
Wave Propagation ◽  
Fundamental Equation ◽  
Stoneley Wave ◽  
Physical Parameters ◽  
Branch Points ◽  
Stoneley Waves ◽  
Interface Waves ◽  
Material Parameters ◽  
Complex Roots ◽  
Wide Range

Abstract The equation governing elastic waves propagating along a solid-solid interface is found to have sixteen (16) independent roots on its eight (8) associated Riemann sheets. The range of existence (in terms of material parameters) for the real root corresponding to the propagation of Stoneley waves has long been known. It is found that outside this range there are two types of behavior. If the material of greater density has a velocity slightly greater than that of the material of lesser density, the unattenuated Stoneley waves make a transition to attenuated Interface waves, i.e., they leak energy away from the interface as they propagate along it. If the more dense material has a velocity more than about three times that of the less dense, then the Interface-wave root disappears and energy is propagated along the interface as Rayleigh waves. This Rayleigh-wave propagation is associated with a different root of the fundamental equation. On the other hand, if the material of greater density has a velocity much lower than that of the material of lower density (a case that is difficult to find physically), then no energy will be propagated along the interface at all. This result was unexpected. Some rather interesting behavior of the 16 roots was noted as the physical parameters were varied over a wide range. In addition to the normal collisions between pairs of roots, and between individual roots and branch points (with attendant Riemann sheet jumping), it was found that some roots go through the point at infinity and return with a change in sign. At least one unexpected case of a multiple root was found. Another case was noted in which a pair of complex roots change quadrants in the complex phase-velocity plane, leading to a discontinuity in root type. Finally, it was noted that, in a cyclic variation of the material parameters, it is possible to choose a path such that the roots, when followed individually, will not return to their original values. In fact, as many as five cycles in parameter space can be accomplished before the roots return. All this strange mathematical behavior seems to have no physical significance, but has been presented to increase understanding of the general behavior of the dispersion relations associated with elastic-wave propagation.

Seismic wave synthesis by Gaussian beam summation: A comparison with finite differences

Geophysics ◽  
1987 ◽  
Vol 52 (8) ◽  
pp. 1065-1073 ◽  
Author(s):  
Th. George ◽  
J. Virieux ◽  
R. Madariaga
Keyword(s):  
Finite Difference ◽  
Gaussian Beam ◽  
Finite Differences ◽  
Fourier Transforms ◽  
Focal Point ◽  
Original Method ◽  
Complex Model ◽  
Summation Method ◽  
Ray Theory ◽  
Head Waves

We apply Gaussian beam summation to the calculation of seismic reflections from complex interfaces, introducing several modifications of the original method. First, we use local geographical coordinates for the representation of paraxial rays in the vicinity of the recording surface. In this way we avoid the time‐consuming evaluation of the ray‐centered coordinates of the observation points. Second, we propose a method for selecting the beams that ensures numerical stability of the synthetic seismograms. Third, we introduce a simple source wave packet that simplifies and stabilizes the calculations of inverse Fourier transforms. We compare reflection seismograms computed using the Gaussian beam‐summation method with those calculated by finite differences. Two simple models are used. The first is a continuous curved interface separating an elastic layer from a free half‐space. A double caustic, or degenerate focal point, appears due to the crossing of reflected rays. In this instance the finite‐difference simulation and the Gaussian beam summation are in excellent agreement. Both phase and amplitude are modeled correctly for both the direct and reverse branches. When compared to geometrical ray theory, Gaussian beam summation provides a good approximation of the field near the caustics while geometrical ray theory does not. The second, more complex, model we consider is a trapezoidal dome with sharp corners in the interface. The corners of the dome in this model produce rather strong diffractions. Also, creeping head waves propagate along the interface. The results compare well with the finite‐difference simulation except for the diffracted branches, where the traveltime of diffracted waves is poorly approximated by the Gaussian beam‐summation method.

Experimental studies on the mechanism of seismoelectric logging while drilling with multipole source

2020 ◽  
Author(s):  
Jun Wang ◽  
Zhenya Zhu ◽  
Wei Guan ◽  
Yongxin Gao ◽  
Xiaorong Wu
Keyword(s):  
Double Layer ◽  
Saturated Porous Medium ◽  
Experimental Studies ◽  
Electric Signal ◽  
Water Tank ◽  
S Wave ◽  
S Waves ◽  
Wave Velocities ◽  
Logging While Drilling ◽  
Full Waveforms

Summary When a seismic wave propagates in a fluid-saturated porous medium, a relative movement forms between the solid and fluid and induces an electric current due to the electronic double layer. As a result, two kinds of seismoelectric coupling responses are generated in this procedure, i.e. the localized electric/magnetic field and interfacial electromagnetic wave field. One important potential application of these two seismoelectric conversions is used for measuring formation P and S waves in well logging. Considering that the strong collar wave seriously affects the velocity measurements of formation P and S waves in current acoustic logging while drilling (LWD), the seismoelectric logging while drilling method, which combines seismoelectric conversion and acoustic LWD technique, was suggested to be a novel method in oil and gas exploration. Because the collar wave can't induce any seismoelectric signal on the metal collar, since there is no double layer formed on a metal surface. In this paper, acoustic and seismoelectric LWD measurements are conducted in the laboratory. We build a scaled multipole acoustic LWD tool to conduct acoustic measurements in a water tank and a sandstone borehole model. We also build a multipole seismoelectric LWD tool and record the seismoelectric signals induced with the same acoustic source. Then we compare the recorded acoustic and seismoelectric signals by using the experimental data. The result indicates that the apparent velocities of seismoelectric signals are equal to the formation P and S wave velocities and the collar waves do not induce any visible electric signal in the full waveforms. We further analyze the mechanism of seismoelectric LWD by a quantitative comparison of the amplitudes between the inner collar wave and outer collar wave. The results show that the amplitude of outer collar wave decreases significantly when it radiates out of the tool, so that the seismoelectric signals induced by collar waves are too weak to be distinguished in the full waveforms of seismoelectric LWD measurements. Thus, the formation P and S wave velocities are detected accurately from the recorded seismoelectric LWD data. These results verify the feasibility of seismoelectric LWD method for measuring acoustic velocities of the borehole formation.

Detection of formation S-wave in a slow formation using a monopole acoustic logging-while-drilling tool

Geophysics ◽  
2018 ◽  
Vol 83 (1) ◽  
pp. D9-D16 ◽  
Author(s):  
Xinding Fang ◽  
Arthur Cheng
Keyword(s):  
Low Frequency ◽  
Stoneley Wave ◽  
Secondary Source ◽  
S Wave ◽  
Drilling Tool ◽  
Acoustic Logging ◽  
Modeling Analysis ◽  
Logging While Drilling ◽  
Refracted Waves ◽  
Drill Collar

Acoustic logging-while-drilling (LWD) is a technology that is used to measure formation elastic properties during drilling. When the formation shear slowness is smaller than the borehole fluid slowness (i.e., fast formation), monopole logging can be used to obtain formation compressional and shear slownesses by measuring the corresponding refracted waves. In a slow formation in which the shear slowness is larger than the borehole fluid slowness, other logging methods, such as quadrupole LWD, are used instead for shear slowness measurement due to the lack of a fully refracted S-wave. Through modeling analysis, we find that the transmitted S-wave generated by a monopole LWD tool in a slow formation can be detected and used to measure the formation shear slowness. This phenomenon can be explained by Huygens’ principle, which states that every point on a wavefront can be considered as a secondary source that induces particle motion. It is hard to discern the transmitted S-wave in monopole wireline data because it strongly interferes with the Stoneley mode in wireline logging. However, the transmitted S-wave decouples from the Stoneley in the LWD environment because the drill collar slows down the low-frequency part of the Stoneley mode. The nondispersive nature of the transmitted S-wave makes it suitable for shear slowness extraction using time semblance analysis, but sophisticated signal preprocessing might be needed because this wave is generally weak compared with the Stoneley wave. Moreover, our study helps us better understand how the Stoneley mode behaves and interferes with other modes in a slow formation under LWD conditions.

Partial Summation Method for XANES Calculation

1997 ◽  
Vol 7 (C2) ◽  
pp. C2-99-C2-102
Author(s):  
T. Fujikawa ◽  
R. Yanagisawa ◽  
N. Yiwata
Keyword(s):  
Summation Method ◽  
Partial Summation

Lean diabetes: A joint analysis of the German DIVE and DPV registries

2017 ◽  
Vol 12 (S 01) ◽  
pp. S1-S84
Author(s):  
B Hartmann ◽  
F Groß ◽  
P Bramlage ◽  
S Lanzinger ◽  
T Danne ◽  
...  
Keyword(s):  
Joint Analysis

The influence of osteopathic correction on the rate of various rhythms of the body

2019 ◽  
pp. 64-71 ◽  
Author(s):  
A. E. Chernikova ◽  
Yu. P. Potekhina
Keyword(s):  
Heart Rate ◽  
Respiratory Rate ◽  
Age Groups ◽  
Biomechanical Properties ◽  
Dispersion Analysis ◽  
The Body ◽  
Body Tissues ◽  
Age Related ◽  
Significant Difference ◽  
Before And After

Introduction. An osteopathic examination determines the rate, the amplitude and the strength of the main rhythms (cardiac, respiratory and cranial). However, there are relatively few studies in the available literature dedicated to the influence of osteopathic correction (OC) on the characteristics of these rhythms.Goal of research — to study the influence of OC on the rate characteristics of various rhythms of the human body.Materials and methods. 88 adult osteopathic patients aged from 18 to 81 years were examined, among them 30 men and 58 women. All patients received general osteopathic examination. The rate of the cranial rhythm (RCR), respiratory rate (RR) heart rate (HR), the mobility of the nervous processes (MNP) and the connective tissue mobility (CTM) were assessed before and after the OC session.Results. Since age varied greatly in the examined group, a correlation analysis of age-related changes of the assessed rhythms was carried out. Only the CTM correlated with age (r=–0,28; p<0,05) in a statistically significant way. The rank dispersion analysis of Kruskal–Wallis also showed statistically significant difference in this indicator in different age groups (p=0,043). With the increase of years, the CTM decreases gradually. After the OC, the CTM, increased in a statistically significant way (p<0,0001). The RCR varied from 5 to 12 cycles/min in the examined group, which corresponded to the norm. After the OC, the RCR has increased in a statistically significant way (p<0,0001), the MNP has also increased (p<0,0001). The initial heart rate in the subjects varied from 56 to 94 beats/min, and in 15 % it exceeded the norm. After the OC the heart rate corresponded to the norm in all patients. The heart rate and the respiratory rate significantly decreased after the OC (р<0,0001).Conclusion. The described biorhythm changes after the OC session may be indicative of the improvement of the nervous regulation, of the normalization of the autonomic balance, of the improvement of the biomechanical properties of body tissues and of the increase of their mobility. The assessed parameters can be measured quickly without any additional equipment and can be used in order to study the results of the OC.

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