scholarly journals Numerical simulations of wave fields for acoustic logging while drilling tools in a fluid-filled trough

2020 ◽  
Author(s):  
Zhifeng Sun ◽  
Xiaoming Tang ◽  
Xiao He ◽  
Xien Liu
Keyword(s):  
Opening Angle ◽  
Asymmetric Structure ◽  
Difference Model ◽  
Acoustic Logging ◽  
Wave Fields ◽  
Wave Speeds ◽  
Drilling Tools ◽  
First Arrival ◽  
Logging While Drilling ◽  
Downhole Measurements

Abstract Examinations of acoustic logging tools in the workshop are significant for checking the performance of every unit before field downhole measurements. It is more convenient to test the tools in a horizontally placed open trough rather than in a vertical closed pipe. To ensure the tools can excite and receive the signals from the trough well (i.e. the pipe waves), we should figure out the wave propagation in such an asymmetric structure. We aim for acoustic logging while drilling (LWD) signals from the fluid-filled trough. Both monopole and quadrupole wave fields are studied through the 3D finite difference model. For monopole acoustic logging, first-arrival full waves are the major concern. The propagation velocities of first-arriving pipe waves do not change with opening angles of the trough. The pipe wave speeds are exactly the same as those in closed pipes of the same sizes; while the amplitudes decrease with increasing opening angles. For quadrupole LWD, velocities of pipe waves have few correlations with opening angles and transducer azimuths. The quadrupole source can even excite the monopole collar waves in the trough, which become the first arrivals of the full waves. The quadrupole pipe waves show a trend of being weaker with increasing opening angles. If the opening angle of the trough is too large, the quadrupole pipe waves could totally be covered by other wavelets. To excite clearer pipe wave signals in the trough, it is suggested that an opening angle as small as possible is optimal for the tests.

scholarly journals Reflection signals and wellbore scattering waves in acoustic logging while drilling

2020 ◽  
Vol 17 (3) ◽  
pp. 552-561
Author(s):  
Yue Pan ◽  
Xiao He ◽  
Hao Chen ◽  
Xiuming Wang
Keyword(s):  
Time Domain ◽  
Body Wave ◽  
Acoustic Signals ◽  
Wave Reflections ◽  
Wave Fields ◽  
S Waves ◽  
Scattering Effects ◽  
Apparent Source ◽  
Logging While Drilling ◽  
Sonic Logging

Abstract In sonic logging while drilling (LWD), it is difficult to extract reflection signals for the goal of geo-steering as the wave fields are so complicated. It is important to analyse the reflection and scattering effects based on the synthetic acoustic signals of the real LWD models, while considering the medium discontinuity at the end of the borehole. We numerically investigate the acoustic LWD responses to reflective boundaries out of the borehole. To simulate the received signals, the 3D finite difference in time domain method is implemented. Mode conversions between the collar and the Stoneley waves are revealed. Strong reflections are generated at the bottom of the well, which can be equivalent to an additional scattering source (i.e. an apparent point source). The scattering waves by the wellbore bottom are generally much stronger than the reflections from the layer interfaces of formations. By comparing the models with stratified interfaces of opposite inclination directions, the propagation mechanisms of two newly recognised reflection waves are revealed in addition to the traditional body wave reflections (P and S waves) in LWD models. The energy of the collar wave radiates outside the borehole and then reflects at the bedding boundaries; meanwhile, the scattering waves from the well bottom can generate reflections too. These reflection arrivals match well with the time predicted by ray theories, respectively. Finally, we propose a possible means to estimate the dipping directions of geological interfaces by reflection waves emitted from both LWD transmitters and the apparent source at the well bottom.

Numerical Study on the Characteristics of Multipole Acoustic Logging While Drilling in Cracked Porous Medium

2014 ◽  
Vol 57 (4) ◽  
pp. 591-606 ◽  
Author(s):  
XU Song ◽  
SU Yuan-Da ◽  
CHEN Xue-Lian ◽  
TANG Xiao-Ming
Keyword(s):  
Porous Medium ◽  
Numerical Study ◽  
Acoustic Logging ◽  
Logging While Drilling

scholarly journals Vibration and horizontal directivity analysis of transmitting transducer for acoustic logging while drilling

2021 ◽  
Vol 18 (3) ◽  
pp. 379-391
Author(s):  
Yang Gou ◽  
Xin Fu
Keyword(s):  
Resonance Frequency ◽  
Wave Equations ◽  
Sound Field ◽  
Frequency Equation ◽  
Acoustic Logging ◽  
Field Radiation ◽  
Transducer Design ◽  
Logging While Drilling ◽  
Vibration Modal ◽  
Radially Polarized

Abstract Radially polarized open-cylindrical piezoelectric transducers are widely used in the field of acoustic logging while drilling (LWD). Unlike the wireline logging transducer, the structure of the acoustic LWD transducer is an open structure; in this case, its radial vibration is accompanied by apparent circumferential vibration. In this paper, based on the two-dimensional wave equations and electrostatic charge equation, according to the free boundary conditions of the transducer, the resonance frequency equation of radial-circumferential coupled vibration for the acoustic LWD transducer is obtained. The vibration modal and resonance frequency for transducers of several typical sizes are simulated using COMSOL software. The results show that when the geometrical size of the transducer satisfies certain conditions, the theoretical calculation and the numerical analysis are in good agreement and the relative error is controlled below 3%. Meanwhile, the horizontal directivity of the LWD transducer after actual installation is discussed, and it is found that adding appropriate coupling materials can improve the monopole sound field radiation. So, it is expected that this work can serve as a reference for the acoustic LWD transducer design and install.

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