scholarly journals Characteristics of elastic wave dispersion and attenuation induced by microcracks in complex anisotropic media

2021 ◽  
Vol 18 (5) ◽  
pp. 788-807
Author(s):  
Xiaobin Li ◽  
Jianguo Yan ◽  
Qiaomu Qi ◽  
Rui Xie
Keyword(s):  
Flow Model ◽  
Fractured Reservoirs ◽  
Laboratory Data ◽  
Low Frequency ◽  
Transversely Isotropic ◽  
Wave Dispersion ◽  
Azimuthal Anisotropy ◽  
Inherent Anisotropy ◽  
Porous Sandstone ◽  
Dispersion And Attenuation

Abstract The mechanism of dispersion and attenuation induced by fluid flow among pores and microcracks in rocks is an important research topic in geophysical domain. A generalised frequency-dependent fourth-rank tensor is proposed and derived herein by combining Sayers's discontinuity tensor formula and Gurevich's squirt flow model. Furthermore, a proposed method for establishing a cracked model with cracks embedded in a transversely isotropic (TI) background medium is developed. Based on the new formulation, we investigate the characteristics of dispersion, attenuation and azimuthal anisotropy of three commonly encountered vertical crack distributions, including aligned cracks, monoclinic cracks and cracks with partial random orientations. We validate the developed model by comparing its predictions with those of the classic anisotropic squirt flow model for an aligned crack. The numerical analyses indicate that the azimuth is independent of frequency when the maximum attenuation is observed for all three crack distributions. In a low-frequency range in the case of an anisotropic background, the attenuation of the qP-wave is inversely proportional to velocity, whereas the attenuation of the qSV-wave is proportional to velocity. In addition, the inherent anisotropy of the rock does not significantly affect the dispersion and attenuation owing to squirt flow. Finally, to investigate the applicability of the theory, we model laboratory data of a synthetic porous sandstone with aligned cracks. Overall, the models agree well with laboratory data. The complex characteristics determined through this study may be useful for the seismic characterisation of fractured reservoirs.

Modeling wave propagation in cracked porous media with penny-shaped inclusions

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. WA141-WA151 ◽  
Author(s):  
Lin Zhang ◽  
Jing Ba ◽  
José M. Carcione ◽  
Weitao Sun
Keyword(s):  
Wave Propagation ◽  
Aspect Ratio ◽  
Crack Density ◽  
Low Frequency ◽  
Confining Pressure ◽  
Wave Dispersion ◽  
Fluid Viscosity ◽  
Porous Rocks ◽  
Flow Models ◽  
Dispersion And Attenuation

Understanding acoustic wave dispersion and attenuation induced by local (squirt) fluid flow between pores and cracks (compliant pores) is fundamental for better characterization of the porous rocks. To describe this phenomenon, some squirt-flow models have been developed based on the conservation of the fluid mass in the fluid mechanics. By assuming that the cracks are represented by isotropically distributed (i.e., randomly oriented) penny-shaped inclusions, this study applies the periodically oscillating squirt flow through inclusions based on the Biot-Rayleigh theory, so that the local squirt flow and global wave oscillation of rock are analyzed in the same theoretical framework of Hamilton’s principle. The governing wave-propagation equations are derived by incorporating all of the crack characteristics (such as the crack radius, crack density, and aspect ratio). In comparison with the previous squirt models, our model predicts the similar characteristics of wave velocity dispersion and attenuation, and our results are in agreement with Gassmann equations at the low-frequency limit. In addition, we find that the fluid viscosity and crack radius only affect the relaxation frequency of the squirt-flow attenuation peak, whereas the crack density and aspect ratio also affect the magnitudes of dispersion and attenuation. The application of this study to experimental data demonstrates that when the differential pressure (the difference between confining pressure and pore pressure) increases, the closure of cracks can lead to a decrease of attenuation. The results confirm that our model can be used to analyze and interpret the observed wave dispersion and attenuation of real rocks.

High‐ and low‐frequency elastic moduli for a saturated porous/cracked rock‐Differential self‐consistent and poroelastic theories

Geophysics ◽  
1996 ◽  
Vol 61 (4) ◽  
pp. 1080-1094 ◽  
Author(s):  
Mickaële Le Ravalec ◽  
Yves Guéguen
Keyword(s):  
Elastic Moduli ◽  
Laboratory Data ◽  
Crack Density ◽  
Low Frequency ◽  
Wave Dispersion ◽  
S Wave ◽  
In Situ Data ◽  
Consistent Model ◽  
Self Consistent ◽  
Theoretical Predictions

Although P‐ and S‐wave dispersion is known to be important in porous/cracked rocks, theoretical predictions of such dispersions have never been given. We report such calculations and show that the predicted dispersions are high in the case of low aspect ratio cracks [Formula: see text] or high crack density [Formula: see text]. Our calculations are derived from first‐principle computations of the high‐ and low‐frequency elastic moduli of a rock permeated by an isotropic distribution of pores or cracks, dry or saturated, with idealized geometry (spheres or ellipsoids). Henyey and Pomphrey developed a differential self‐consistent model that is shown to be a good approximation. This model is used here, but as it considers cracks with zero thickness, it can not account for fluid content effects. To remove this difficulty, we combine the differential self‐consistent approach with a purely elastic calculation of moduli in two cases: that of spherical pores and that of oblate spheroidal cracks with a nonzero volume. This leads to what we call the “extended differential, self‐consistent model” (EM). When combining these EM results with the Gassmann equation, it is possible to derive and compare the theoretical predictions for high‐ and low‐frequency effective moduli in the case of a saturated rock. Since most laboratory data are ultrasonic measurements and in situ data are obtained at much lower frequencies, this comparison is useful for interpreting seismic data in terms of rock and fluid properties. The predicted dispersions are high, in agreement with previous experimental results. A second comparison is made with the semi‐empirical model of Marion and Nur, which considers the effects of a mixed porosity (round pores and cracks together).

Hole geometry and anisotropic effects on tube‐wave propagation: A quasi‐static study

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 167-175 ◽  
Author(s):  
L. M. A. Nicoletis ◽  
A. Bamberger ◽  
J. A. Quiblier ◽  
P. Joly ◽  
M. Kern
Keyword(s):  
Wave Velocity ◽  
Low Frequency ◽  
Transversely Isotropic ◽  
Tectonic Stress ◽  
Azimuthal Anisotropy ◽  
Transversely Isotropic Medium ◽  
Wave Characteristics ◽  
Stress Directions ◽  
Borehole Breakouts ◽  
Tube Wave

Tube‐wave characteristics, namely velocity and polarization, are affected by borehole anomalies related to nonhydrostatic tectonic stress. The anomalies we consider are borehole ellipticity, azimuthal anisotropy as modeled by a rotated transversely isotropic medium, and borehole breakouts as modeled by local heterogeneities in elastic properties. The low‐frequency tube‐wave velocity is obtained by a variational approach to a plane‐strain, static‐equilbrium problem. We solve the problem with hole ellipticity analytically and the problem with azimuthal anisotropy numerically by a finite‐element method. The results show that weak ellipticity has a negligible effect on the tube‐wave velocity: a relative variation of 10 percent in the main diameters of the hole produces a perturbation of only 0.5 percent in the velocity. However, localized damage to the hole can reduce tube‐wave velocity significantly. Furthermore, for tube‐wave polarization, it is unrealistic to obtain deviations from the radial direction greater than 15 degrees, which makes it difficult to obtain any valuable information on the stress directions from the tube wave.

Methods to isolate retrograde and prograde Rayleigh-wave signals

2019 ◽  
Vol 219 (2) ◽  
pp. 975-994 ◽  
Author(s):  
Gabriel Gribler ◽  
T Dylan Mikesell
Keyword(s):  
Rayleigh Wave ◽  
Time Domain ◽  
Fundamental Mode ◽  
Poisson Ratio ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Low Frequencies ◽  
Retrograde Motion ◽  
Mode Identification ◽  
Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

scholarly journals Wave Dispersion and Attenuation on Human Femur Tissue

Sensors ◽  
2014 ◽  
Vol 14 (8) ◽  
pp. 15067-15083 ◽  
Author(s):  
Maria Strantza ◽  
Olivia Louis ◽  
Demosthenes Polyzos ◽  
Frans Boulpaep ◽  
Danny van Hemelrijck ◽  
...  
Keyword(s):  
Wave Dispersion ◽  
Human Femur ◽  
Dispersion And Attenuation

Application of Low-Frequency Energy Increment Technology in Hydrocarbon Prediction

2012 ◽  
Vol 472-475 ◽  
pp. 178-182
Author(s):  
Zhi Ming Li ◽  
Xue Yan Hu ◽  
Ling Xia Zhen
Keyword(s):  
Laboratory Data ◽  
Low Frequency ◽  
Biot Theory ◽  
Hydrocarbon Detection ◽  
Hydrocarbon Prediction ◽  
Phase Medium ◽  
Multi Phase ◽  
Cave Detection ◽  
Fluid Detection ◽  
Energy Increment

Based on the Biot theory and laboratory data, engineers of LandOcean recently develop a certain technology for hydrocarbon detection in multi-phase medium in order to reduce ambiguity and uncertainty. The sensitivity of the technology is superior to others especially in carbonate pores and cave detection, igneous hydrocarbon prediction and fluid detection of non-well areas. A number of projects and wells drilling proved that this technology is effective and reliable.

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