Attenuation mechanisms in sands: Laboratory versus theoretical (Biot) data

Prasad, Manika; Meißner, R.

doi:10.1190/1.1443284

Cited by 109 publications

(76 citation statements)

References 12 publications

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“…Results and discussion 3.1. Grain size effect Vp seems to be affected by grain size and porosity ( Figure 2b shows Vp in Z direction, Vpz): velocities in the coarse-grained sample (with lower porosity) are slightly higher than in the fine-grained sample, which agrees with Prasad and Meissner (1992).…”

Section: Samples and Sample Preparationsupporting

confidence: 76%

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2003

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As part of our study on "Relationships between seismic properties and rock microstructure", we have studied 1. Methods for detection of stress-induced velocity anisotropy in sands.2. We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments. INTRODUCTIONIn this quarter, we submit results of our research on: pore textural mapping and its relation to centimeter-scale core measurements of impedance and measurements of seismic properties of unconsolidated sediments at very low effective pressures. The special effect of stress anisotropy on velocity anisotropy is investigated. Two papers have been submitted for publication. This report presents preprints of our research relevant to this project on impedance mapping, soft-sediment measurements, stress anisotropy, and scale effects. PAPER 1Vega, S., Prasad, M., Mavko, G., and Nur, A., Detection of stress-induced velocity anisotropy in sands. Submitted to GRL In this paper, we present a preliminary study on stress-induced velocity anisotropy in two different sands. We describe the method used for sample preparation, and the polyaxial apparatus used for velocity, strain, and stress measurements. Furthermore, we examine the velocity response as a function of stress in different directions of applying uniaxial strain test to the samples. The strains and velocities of the two sands are also compared. We show that stress-induced velocity anisotropy exists and is detectable in sands. A stress anisotropy of 87% corresponds to a velocity anisotropy of 29%-34%, and there is a linear dependency of velocity anisotropy on stress anisotropy in the sands. We apply different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. Characterizing and understanding the microgeometry, their textures, scales, and textural anisotropy is important for better understanding the role of microgeometry on effective elastic properties. We analyzed SAM images from Bakken shale, Bazhenov shale, and Woodford shale. Our analysis, based on spatial autocorrelation functions shows that there is a small positive correlation between the degree of heterogeneity and the mean spatial correlation length of the microstructure. The textural anisotropy ranges from 10% to 80%. There is considerable variability within each image, as well as from one image to another. A singular value decomposition (SVD) spectral analysis showed that the shale microstructures have characteristics in common with fractal stochastic images. We also obtain a correlation between maturity and textural heterogeneity. The textural heterogeneity increases with increasing maturity (decreasing kerogen content), while there is a general decrease in textural anisotropy with maturity. The accompanying paper A4 in this volume relates the textural characteristics obtained from image processing ...

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Section: Samples and Sample Preparationsupporting

confidence: 76%

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2003

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“…The velocity data are very consistent between different samples and between different pressure cycles for the same sample. They also agree well with similar sand data from Domenico (1976), Prasad and Meissner (1992), Yin (1992), and Robertson et al (1995). Solid lines in Figure 7 represent empirical fits to the data.…”

Section: Seismic Properties Of Sands At Very Low Pressuressupporting

confidence: 75%

Seismic and Rockphysics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2002

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As part of our study on Relationships between seismic properties and rock microstructure , we have studied kerogen-rich shales using Scanning Acoustic Microscopy and ultrasonic wave propagation. We show quantification of microstructure in kerogen shales as variations in acoustic impedance using scanning acoustic microscopy (SAM). The acoustic maps are used to understand the seismic response of the rock using ultrasonic wave propagation. We show examples of impedance maps in kerogen-rich shales with acoustic microscopy kerogen shales along with velocity measurements on core-plugs. We also show that an increase in elastic modulus with increasing kerogen maturity can be directly related to the microstructural acoustic impedance changes. A positive relation is established between microstructural changes and velocity variations as functions of kerogen maturity.Secondly, we have initiated measurements on sands as part of our study on Seismic properties of Ultra-deep-water sediments . We present the instrument design and initial results here.

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“…Figure 1 shows the P-and S-wave velocities plotted against pressure for all our samples, and for measurements on clean sands from Prasad and Meissner (1992), Domenico (1977), Yin (1992), Estes et al (1994), and Robertson et al (1995). This figure demonstrates similar trends between the data from all sources.…”

Section: The Leading Edge February 2002 February 2002 the Leading Edgsupporting

confidence: 64%

Seismic and Rockphysics Diagnostics of Multiscale Reservoir Textures

Mavko¹

2002

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As part of our study on "Relationships between seismic properties and rock microstructure", we have studied 1. Kerogen-rich shales using Scanning Acoustic Microscopy and ultrasonic wave propagation. We find that an increase in elastic modulus with increasing kerogen maturity can be directly related to the microstructural acoustic impedance changes. A positive relation is established between microstructural changes and velocity variations as functions of kerogen maturity. 2. Elastic properties of clay minerals using Atomic Force Acoustic Microscopy and Scanning Acoustic Microscopy. We show the effect of clay minerals in contact zones as load-bearing constituents of rocks 3. Elastic properties of unconsolidated sediments in an effort to quantify attributes for detection of overpressures from seismic and for effects of stress-induced velocity anisotropy in sediments 4. We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments.4 INTRODUCTIONIn this quarter, we submit results of our research on: impedance mapping on a micrometer scale and its relation to centimeter-scale core measurements of impedance, measurements of clay modulus using Atomic Force Acoustic Microscopy (AFAM) and measurements of seismic properties of unconsolidated sediments at very low effective pressures. Five papers have been published on the work done in the first year of this project. This report presents reprints of our publications relevant to this project on impedance mapping, AFAM measurements, and overpressure analyses. 7 PAPER 1Prasad, M., Reinstaedtler, M., Nur, A., and Walter A.: Quantitative Acoustic Microscopy: Application to Petrophysical Studies of Reservoir Rocks: Acoustical Imaging, Vol. 26,[493][494][495][496][497][498][499][500][501][502] We demonstrate here applications of scanning acoustic microscopy (SAM) to quantify microstructure as variations in acoustic impedance. The acoustic maps can then be used to understand the seismic response of the rock. For example, ultrasonic measurements on kerogen shales have shown that the elastic modulus increases with increasing kerogen maturity. SAM of these shales shows a stiffening of the shale framework with increasing kerogen maturity. The load-bearing material changes from low impedance kerogen to high impedance shale. The impedance values determined from SAM are comparable with those obtained from ultrasonic time-of-flight data. In contrast, the cement is load bearing in sandstones where high impedance quartz grains are cemented together by low impedance clay. The cement determines not only the total impedance of the rock but also its pressure dependence.Paper 1: Total of eight figures in paper 8 PAPER 2Zimmer, M., Prasad, M., and Mavko, . Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, Paper RP2.5. Presence of clay minerals, hydrous aluminosilicates with grain size smaller than 2 mm, We develope...

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Attenuation mechanisms in sands: Laboratory versus theoretical (Biot) data

Cited by 109 publications

References 12 publications

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Seismic and Rockphysics Diagnostics of Multiscale Reservoir Textures

Seismic and Rockphysics Diagnostics of Multiscale Reservoir Textures

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