Azimuthally Focused LWD Sonic Logging for Shear Wave Anisotropy Measurement and Borehole Imaging

Author(s):  
Medhat Mickael ◽  
Craig Barnett ◽  
Mohamed Diab
Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1627-1633 ◽  
Author(s):  
Bart W. Tichelaar ◽  
Klaas W. van Luik

Borehole sonic waveforms are commonly acquired to produce logs of subsurface compressional and shear wave velocities. To this purpose, modern borehole sonic tools are usually equipped with various types of acoustic sources, i.e., monopole and dipole sources. While the dipole source has been specifically developed for measuring shear wave velocities, we found that the dipole source has an advantage over the monopole source when determining compressional wave velocities in a very slow formation consisting of unconsolidated sands with a porosity of about 35% and a shear wave velocity of about 465 m/s. In this formation, the recorded compressional refracted waves suffer from interference with another wavefield component identified as a leaky P‐wave, which hampers the determination of compressional wave velocities in the sands. For the dipole source, separation of the compressional refracted wave from the recorded waveforms is accomplished through bandpass filtering since the wavefield components appear as two distinctly separate contributions to the frequency spectrum: a compressional refracted wave centered at a frequency of 6.5 kHz and a leaky P‐wave centered at 1.3 kHz. For the monopole source, the frequency spectra of the various waveform components have considerable overlap. It is therefore not obvious what passband to choose to separate the compressional refracted wave from the monopole waveforms. The compressional wave velocity obtained for the sands from the dipole compressional refracted wave is about 2150 m/s. Phase velocities obtained for the dispersive leaky P‐wave excited by the dipole source range from 1800 m/s at 1.0 kHz to 1630 m/s at 1.6 kHz. It appears that the dipole source has an advantage over the monopole source for the data recorded in this very slow formation when separating the compressional refracted wave from the recorded waveforms to determine formation compressional wave velocities.


Geophysics ◽  
2020 ◽  
pp. 1-91
Author(s):  
Ruijia Wang ◽  
Brian Hornby ◽  
Kristoffer Walker ◽  
Chung Chang ◽  
Gary Kainer ◽  
...  

Real-time open hole wireline sonic logging data processing becomes a nontrivial task to accurately, automatically and efficiently evaluate both the compressional and shear slowness of a borehole rock formation when human interaction is not possible and signal processing time is limited to elapsed time between different transmitter firings. To address real-time sonic data processing challenges, we present self-adaptive, data-driven methods to accurately measure formation compressional and shear wave slowness from both monopole and dipole waveforms in all types of formations. These new real-time processing techniques take advantage of the fact that advanced wireline sonic logging tools have wide frequency responses and little to no detectable tool body arrivals. These technology improvements provide an opportunity to implement a first-motion-detection technique that detects the onset of compressional waves in the monopole array waveforms. The knowledge of compressional arrival time and corresponding slowness are then used to project an appropriate slowness-time window in order to identify the monopole refracted shear wave and its slowness based on the range of possible Vp/Vs for earth rock formation. To process the borehole dipole flexural waves, we provide a new, data-driven frequency domain method that enables the evaluation of the full flexural-wave dispersion response and its corresponding low-frequency shear slowness asymptote. Field data processing results show that our methods provide high-quality compressional slowness (DTC) and shear slowness(DTS) measurements that are not affected by other borehole modes or dispersion complications in all formation types.


Geophysics ◽  
1989 ◽  
Vol 54 (5) ◽  
pp. 590-597 ◽  
Author(s):  
S. T. Chen

This paper provides laboratory verification of a novel technique for direct, on‐line, shear (S)-wave velocity logging in hard and soft formations using a quadrupole source as recently suggested by theory. Conventional monopole logging tools are not capable of directly measuring the shear‐wave velocity in soft formations. Previous theoretical and laboratory experimental work has already shown that a dipole source can be used for direct shear‐wave velocity logging in hard and soft formations. I demonstrate in this paper that quadrupole sources can also achieve this objective. Furthermore, the quadrupole source can produce higher resolution of S-wave velocity, since it can be operated at higher frequencies. A power comparison of monopole, dipole, and quadrupole indicates that a field quadrupole logging tool may be expected to produce strong enough signals for practical operation. The present studies were conducted on laboratory scale models representative of sonic logging conditions in the field. I used a limestone model to represent hard formations and a plastic model to simulate a soft formation such as Gulf Coast soft shale or near‐surface materials.


2019 ◽  
Vol 146 (2) ◽  
pp. EL129-EL134 ◽  
Author(s):  
Chunxi Zhuang ◽  
Song Xu ◽  
Huanran Li ◽  
Yuanda Su ◽  
Xiaoming Tang

2012 ◽  
Author(s):  
Medhat W. Mickael ◽  
Craig Barnett ◽  
Mohamed Salah Diab

Author(s):  
Anders Batman Mjelle ◽  
Anesa Mulabecirovic ◽  
Roald Flesland Havre ◽  
Edda Jonina Olafsdottir ◽  
Odd Helge Gilja ◽  
...  

Abstract Purpose Liver elastography is increasingly being applied in screening for and follow-up of pediatric liver disease, and has been shown to correlate well with fibrosis staging through liver biopsy. Because time is of the essence when examining children, we wanted to evaluate if a reliable result can be achieved with fewer acquisitions. Materials and Methods 243 healthy children aged 4–17 years were examined after three hours of fasting. Participants were divided into four age groups: 4–7 years; 8–11 years; 12–14 years and 15–17 years. Both two-dimensional shear wave elastography (2D-SWE; GE Logiq E9) and point shear wave elastography (pSWE; Samsung RS80A with Prestige) were performed in all participants, while transient elastography (TE, Fibroscan) was performed in a subset of 87 children aged 8–17 years. Median liver stiffness measurement (LSM) values of 3, 4, 5, 6, 7, and 8 acquisitions were compared with the median value of 10 acquisitions (reference standard). Comparison was performed for all participants together as well as within every specific age group. We investigated both the intraclass correlation coefficient (ICC) with absolute agreement and all outliers more than 10 %, 20 % or ≥ 0.5 or 1.0 kPa from the median of 10 acquisitions. Results For all three systems there was no significant difference between three and ten acquisitions, with ICCs ≥ 0.97. All systems needed 4 acquisitions to achieve no LSM deviating ≥ 1.0 kPa of a median of ten. To achieve no LSM deviating ≥ 20 % of a median of ten acquisitions, pSWE and TE needed 4 acquisitions, while 2D-SWE required 6 acquisitions. Conclusion Our results contradict recommendations of 10 acquisitions for pSWE and TE and only 3 for 2D-SWE.


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