Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation

Figueiredo, José J. S. de; Schleicher, Jörg; Stewart, Robert R.; Dayur, N.; Omoboya, Bode; Wiley, Robert W.; William, A.

doi:10.1093/gji/ggs130

Cited by 37 publications

(18 citation statements)

References 29 publications

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“…A convenient way to conduct experiments under well‐controlled conditions involves the use of synthetic materials for which the microstructure is well characterized and reproducible. Several attempts have been reported in the literature for manufacturing synthetic rocks with controlled microstructures that are simpler to analyze than typical microstructures found in natural rocks [e.g., Ass’ad et al ., , ; Rathore et al ., ; Tillotson et al ., , ; Stewart et al ., ; De Figueiredo et al ., , ; Amalokwu et al ., ; Ding et al ., ]. The manufacturing process of these synthetic rocks allows for a relatively accurate control of the final microstructure.…”

Section: Introductionmentioning

confidence: 99%

Stress‐dependent permeability and wave dispersion in tight cracked rocks: Experimental validation of simple effective medium models

et al. 2017

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We experimentally assess the impact of microstructure, pore fluid, and frequency on wave velocity, wave dispersion, and permeability in thermally cracked Carrara marble under effective pressure up to 50 MPa. The cracked rock is isotropic, and we observe that (1) P and S wave velocities at 500 kHz and the low‐strain (<10−5) mechanical moduli at 0.01 Hz are pressure‐dependent, (2) permeability decreases asymptotically toward a small value with increasing pressure, (3) wave dispersion between 0.01 Hz and 500 MHz in the water‐saturated rock reaches a maximum of ~26% for S waves and ~9% for P waves at 1 MPa, and (4) wave dispersion virtually vanishes above ~30 MPa. Assuming no interactions between the cracks, effective medium theory is used to model the rock's elastic response and its permeability. P and S wave velocity data are jointly inverted to recover the crack density and effective aspect ratio. The permeability data are inverted to recover the cracks' effective radius. These parameters lead to a good agreement between predicted and measured wave velocities, dispersion and permeability up to 50 MPa, and up to a crack density of ~0.5. The evolution of the crack parameters suggests that three deformation regimes exist: (1) contact between cracks' surface asperities up to ~10 MPa, (2) progressive crack closure between ~10 and 30 MPa, and (3) crack closure effectively complete above ~30 MPa. The derived crack parameters differ significantly from those obtained by analysis of 2‐D electron microscope images of thin sections or 3‐D X‐ray microtomographic images of millimeter‐size specimens.

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Section: Introductionmentioning

confidence: 99%

Stress‐dependent permeability and wave dispersion in tight cracked rocks: Experimental validation of simple effective medium models

et al. 2017

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“…For cracked sample with single diameter, the crack density parameter is given by

e_{c} = N \frac{π h_{i} r_{i}^{2}}{V_{m}},

where N is the total number of inclusions in the model of radius r i , h i is the thickness (or crack aperture) of crack and V m is the volume of the cracked model region for each sample (De Figueiredo et al . ).…”

Section: Methodsmentioning

confidence: 97%

“…The effect of the source frequency on Thomsen's parameter (γ) estimation, as well as the scattering shear wave attenuation due to fractures, was investigated by De Figueiredo et al . (). Although these studies used synthetic rock samples different to real rocks, these models provided an understanding of the elastic anisotropy and helped to calibrate numerical models.…”

Section: Introductionmentioning

confidence: 97%

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Henriques

Figueiredo

Santos

et al. 2017

Geophysical Prospecting

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A B S T R A C TPhysical modelling of cracked/fractured media using downscaled laboratory experiments has been used with great success as a useful alternative for understanding the effect of anisotropy in the hydrocarbon reservoir characterization and in the crustal and mantle seismology. The main goal of this work was to experimentally verify the predictions of effective elastic parameters in anisotropic cracked media by Hudson and Eshelby-Cheng's effective medium models. For this purpose, we carried out ultrasonic measurements on synthetic anisotropic samples with low crack densities and different aspect ratios. Twelve samples were prepared with two different crack densities, 5% and 8%. Three samples for each crack density presented cracks with only one crack aspect ratio, whereas other three samples for each crack density presented cracks with three different aspect ratios in their composition. It results in samples with aspect ratio values varying from 0.13 to 0.26. All the cracked samples were simulated by penny-shaped rubber inclusions in a homogeneous isotropic matrix made with epoxy resin. Moreover, an isotropic sample for reference was constructed with epoxy resin only. Regarding velocity predictions performed by the theoretical models, Eshelby-Cheng shows a better fit when compared with the experimental results for samples with single and mix crack aspect ratio (for both crack densities). From velocity values, our comparisons were also performed in terms of the ε, γ , and δ parameters (Thomsen parameters). The results show that Eshelby-Cheng effective medium model fits better with the measurements of ε and γ parameters for crack samples with only one type of crack aspect ratio.

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“…Many types of methods have been used to evaluate fractures in seismic exploration (Li 1997;Zhao et al 2014;Kong et al 2012). Among these, the compressional wave anisotropy Ass'ad et al 1992) and shear wave splitting (Baird et al 2015;de Figueiredo et al 2013;Guéguen and Sarout 2012) are the most widely used methods at the present time to evaluate fractures. The anisotropy and fracture parameters were obtained by seismic prospecting.…”

Section: Introductionmentioning

confidence: 99%

Experiments on acoustic measurement of fractured rocks and application of acoustic logging data to evaluation of fractures

et al. 2017

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Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoir core samples to investigate true underground conditions. Due to the diversity of the fracture parameters, the simulation and evaluation of fractured rock in the laboratory setting is also difficult. Previous researchers have typically used a single material, such as resin, to simulate fractures. There has been a great deal of simplifying of the materials and conditions, which has led to disappointing results in application. In the present study, sandstone core samples were selected and sectioned to simulate fractures, and the changes of the compressional and shear waves were measured with the gradual increasing of the fracture width. The effects of the simulated fracture width on the acoustic wave velocity and amplitude were analyzed. Two variables were defined: H represents the amplitude attenuation ratio of the compressional and shear wave, and x represents the transit time difference value of the shear wave and compressional wave divided by the transit time of the compressional wave. The effect of fracture width on these two physical quantities was then analyzed. Finally, the methods of quantitative evaluation for fracture width with H and x were obtained. The experimental results showed that the rock fractures linearly reduced the velocity of the shear and compressional waves. The effect of twin fractures on the compressional velocity was almost equal to that of a single fracture which had the same fracture width as the sum of the twin fractures. At the same time, the existence of fractures led to acoustic wave amplitude attenuations, and the compressional wave attenuation was two times greater than that of the shear wave. In this paper, a method was proposed to calculate the fracture width with x and H, then this was applied to the array acoustic imaging logging data. The application examples showed that the calculated fracture width could be compared with fractures on the electric imaging logs. These rules were applied in the well logs to effectively evaluate the fractures, under the case of no image logs, which had significance to prospecting and development of oil and gas in fractured reservoirs.

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Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation

Cited by 37 publications

References 29 publications

Stress‐dependent permeability and wave dispersion in tight cracked rocks: Experimental validation of simple effective medium models

Stress‐dependent permeability and wave dispersion in tight cracked rocks: Experimental validation of simple effective medium models

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Experiments on acoustic measurement of fractured rocks and application of acoustic logging data to evaluation of fractures

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