Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

Wang, Hua; Tao, Guo; Shang, Xuefeng; Fang, Xinding; Burns, Daniel R.

doi:10.1007/s11770-013-0400-6

Cited by 23 publications

(6 citation statements)

References 45 publications

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“…In our previous study (Wang et al, 2013a), we use a 3D FEM to simulate the wavefield rather than a staggered finite-difference method (FDM) (e.g., Wang et al, 2013b). FEM was shown to be reliable, but the computational cost is too high to allow a large number of simulations to be conducted.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the high-frequency wavefield of an off-center monopole acoustic logging-while-drilling tool

2015

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During logging-while-drilling (LWD) operations, complex drill string movements and the weight of the drill pipe often lead to a measurement tool that is not centralized. Therefore, studies of the response of an off-center acoustic LWD tool are essential to facilitate better interpretation of measurements made in an actual drilling environment. Such studies will be helpful for tool design and data processing. We used a finite-difference method to simulate the response of a noncentralized monopole acoustic LWD tool at high frequency (10 kHz). We analyzed the effects on the waveforms for receivers at different azimuths caused by an off-center tool with differing amounts of offset. We used velocity-time semblance and dispersion analysis methods to help us to understand the modes in the waveforms at different azimuth receivers for different tool offsets. We have found that the waveforms in the direction of the tool offset, that is, where the fluid column is smallest, were affected the most. Waveforms in the orthogonal direction were less affected by tool offset. Collar flexural and collar quadrupole modes appear when the tool is off center. In addition, the formation flexural and quadrupole modes contaminate the Stoneley wave. Waveforms in a fast formation are more strongly affected by the offset of the tool than those in a slow formation. In a fast formation, the new collar modes make it difficult to determine the P-wave velocity in the direction of tool offset whereas it is easier in the orthogonal direction. However, P-waves are less contaminated by new modes in a slow formation. Due to the significant changes in waveforms with azimuth when the tool is off center, the simple addition of all waveforms from an azimuthal distribution of receivers will not result in a clean waveform that is sensitive to only the surrounding formation.

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Section: Introductionmentioning

confidence: 99%

Investigation of the high-frequency wavefield of an off-center monopole acoustic logging-while-drilling tool

2015

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“…The source is located at z ¼ 0 m, and the receivers at eight different offsets are located from z ¼ 3 m to z ¼ 4.05 m with a minimum sourcereceiver spacing of 3 m and receiver offset separation of 0.15 m along the borehole. The complex frequency-shifted perfectly matched layer method (with the absorbing layers of 20 grids on each side of the 3D model) is used to eliminate the reflection from the truncated boundary of the simulation region (Wang et al, 2013b). In the following discussion, we shift the entire tool to an equal amount moving receiver 1 toward the edge of the borehole (positive direction of x-axis).…”

Section: Methods and Modelmentioning

confidence: 99%

Reliability of velocity measurements made by monopole acoustic logging-while-drilling tools in fast formations

2017

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The accuracy of velocity measurements made using a monopole acoustic logging-while-drilling (ALWD) measurement tool is influenced by the eccentering of the tool due to complex drill string movements. We have used the velocity of collar flexural mode (at the source frequency range) as a reference and classified the fast formations into (1) fast-fast (FF) formations with compressional velocity far larger than the collar flexural velocity and (2) slow-fast (SF) formations with compressional velocity approaching that of the collar flexural velocity. We use a 3D finite-difference method to simulate the response of an eccentered monopole ALWD tool with different eccentering magnitudes (offsets) for the two types of formations to facilitate better interpretation of velocity measurements made in an actual drilling environment. We find that the collar extensional mode, existing in the centralized and eccentered tool cases, only affects the formation P-wave measurement and can be eliminated by using an isolator. The collar flexural mode, which is a shear motion in the collar and can only be excited in a centralized tool by a dipole source, is also excited when a monopole tool is eccentered, and it significantly affects the measurement of the compressional velocity in the SF formation and that of the shear velocity in the FF formation, even for small eccentering offsets. Thus, the uncorrected monopole ALWD tool provides unreliable formation velocities (either the compressional or shear velocities) in fast formations because of the significant influence of the tool offsets on the measurement. To minimize the influence of tool offset on the measurements, we compared the differences between the waveforms collected for different azimuths and tool offsets and the centralized monopole waveforms.

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“…7). In the FD simulation, we use a complex frequency shift perfectly matched layer method (CFS-PML) to ensure the stability in a high contrast model and the complete absorption from the truncated boundary (Wang et al, 2011;Wang et al, 2013). To generate a directional source, we use multiple point sources in the FD and the amplitudes of the different point sources are tapered from the center to the edges by using a Hanning window [as shown in Fig.…”

Section: Wavefield For the Pitch-catch Methodsmentioning

confidence: 99%

Understanding acoustic methods for cement bond logging

Wang¹,

Guo²,

Shang³

2016

The Journal of the Acoustical Society of America

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Well cementation is important for oil/gas production, underground gas storage, and CO2 storage, since it isolates the reservoir layers from aquifers to increase well integrity and reduce environmental footprint. This paper analyzes wave modes of different sonic/ultrasonic methods for cement bonding evaluation. A Two dimensional finite difference method is then used to simulate the wavefield for the ultrasonic methods in the cased-hole models. Waveforms of pulse–echo method from different interfaces in a good bonded well are analyzed. Wavefield of the pitch–catch method for free casing, partial or full bonded models with ultra-low density cement are studied. Based on the studies, the modes in different methods are considered as follows: the zero-order symmetric Leaky–Lamb mode (S0) for sonic method, the first-order symmetric Leaky–Lamb mode (S1) for the pulse–echo method, and the zero-order anti-symmetric Leaky–Lamb mode (A0) for the pitch–catch method. For the sonic method, a directional transmitter in both the azimuth and axial directions can generate energy with a large incidence angle and azimuth resolution, which can effectively generate S0 and break out the azimuth limitation of the conventional sonic method. Although combination of pulse–echo and pitch–catch methods can determine the bonding condition of the third interface for the ultra-low density cement case, the pitch–catch cannot tell the fluid annulus thickness behind casing for the partial bonded cased-hole.

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Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

Cited by 23 publications

References 45 publications

Investigation of the high-frequency wavefield of an off-center monopole acoustic logging-while-drilling tool

Investigation of the high-frequency wavefield of an off-center monopole acoustic logging-while-drilling tool

Reliability of velocity measurements made by monopole acoustic logging-while-drilling tools in fast formations

Understanding acoustic methods for cement bond logging

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