Simultaneous measurements of elastic wave velocities and electrical conductivity in a brine-saturated granitic rock under confining pressures and their implication for interpretation of geophysical observations

Watanabe, Tohru; Higuchi, A.

doi:10.1186/s40645-015-0067-0

Cited by 26 publications

(27 citation statements)

References 26 publications

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“…In this model, a transversely isotropic symmetry and a lack of interaction between individual cracks were assumed. The crack‐free properties of Aji granite were used from velocity measurements of hydrostatic experiments at 177 MPa, under which conditions most of the microcracks are closed: E 0 = 80.3 GPa and ν 0 = 0.242 (Watanabe & Higuchi, ). The saturation parameter δ is defined as follows:

δ = \frac{9 normalπ ((), 1 - 2 ν_{0})}{16 ((), 1 - {ν_{0}}^{2})} \frac{K_{0}}{K_{normalf}} α,

where K 0 and K f are the bulk moduli of the solid matrix and fluid, respectively, and α is the crack aspect ratio.…”

Section: Discussionmentioning

confidence: 99%

Evolution of Elastic Wave Velocities and Amplitudes During Triaxial Deformation of Aji Granite Under Dry and Water‐Saturated Conditions

Zaima

Katayama

2018

JGR Solid Earth

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Elastic wave velocities and amplitudes in fine‐grained Aji granite are measured during a series of deformation experiments under both dry and fluid‐saturated conditions, where compressional and shear waves traveled in a direction normal to the compressional axis, and shear wave was polarized normal to the compressional axis. In the early stages of deformation, both VP and VS increase slightly due to closure of preexisting cracks and then decrease due to nucleation and crack growth as the sample approaches failure. During deformation, the different sensitivities of compressional and shear waves to fluid‐filled cracks mean that the ratio VP/VS tends to increase for wet experiments and decrease for dry experiments prior to failure. The relative changes in elastic wave amplitudes are also related to deformation and fluid saturation: amplitude decreases at high differential stresses due to the opening of cracks oriented subparallel to the axis of maximum compression, whereas a relatively minor change in amplitude was observed under fluid‐saturated conditions. Thus, the changes in velocity and amplitude during the deformation experiments are linked to crack development and geometry. However, this sensitivity differs between dry and fluid‐saturated conditions. The monitoring of fluid injection volumes during fluid‐saturated experiments shows that decreasing elastic wave velocities and amplitudes coincide with increasing fluid injection. These systematic relationships among elastic wave velocity, amplitude, crack development, and fluid saturation suggest that understanding changes in seismic wave properties can offer significant insights into the temporal changes in the structure of fracture zones.

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δ = \frac{9 normalπ ((), 1 - 2 ν_{0})}{16 ((), 1 - {ν_{0}}^{2})} \frac{K_{0}}{K_{normalf}} α,

where K 0 and K f are the bulk moduli of the solid matrix and fluid, respectively, and α is the crack aspect ratio.…”

Section: Discussionmentioning

confidence: 99%

Evolution of Elastic Wave Velocities and Amplitudes During Triaxial Deformation of Aji Granite Under Dry and Water‐Saturated Conditions

Zaima

Katayama

2018

JGR Solid Earth

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“…In this case, only the interconnected sheets exist. Because microcracks are pressure dependent, both hydraulic (e.g., Benson, Schubnel, et al, ; Benson, Meredith, & Schubnel, ) and electrical (e.g., Watanabe & Higuchi, ) transport properties are dramatically affected by confining pressure. In this second case scenario, considering the crack (or sheets) opening w , simple calculations (Guéguen & Dienes, ) give κ c ~ w 3 and F c ~ ϕ c −1 ~ w −1 .…”

Section: Discussion: Pressure Dependence Of Transport Propertiesmentioning

confidence: 99%

“…Microcracks have been recognized as a major contributor to the pressure dependence of the elastic properties of rocks (e.g., Walsh, ). Similarly, permeability (e.g., Benson, Schubnel, et al, ; Brace et al, ; Faoro et al, ; Guéguen & Schubnel, ; Schubnel et al, ; Walsh & Brace, ) and electrical resistivity (e.g., Daily & Lin, ; Fredrich, Greaves, & Martin, ; Han et al, , ; Kaselow & Shapiro, ; Milsch et al, ; Violay et al, ; Watanabe & Higuchi, ) were also shown to be pressure‐dependent properties. In nonporous microcracked rocks, the pressure‐induced variations in permeability can reach several orders of magnitudes and are attributed to the closure of existing microcracks (e.g., Benson, Schubnel, et al, ; Benson, Meredith, et al, ; Schubnel et al, ).…”

Section: Introductionmentioning

confidence: 96%

Pressure‐Dependent Elastic and Transport Properties of Porous and Permeable Rocks: Microstructural Control

et al. 2017

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Although several studies aimed at linking electrical and hydraulic transport properties in rocks, the existing models remain at most incomplete. Based on this observation, in addition to the transport properties, this contribution investigates the pressure dependence of P wave velocities and porosity for three porous rocks. Apart from hydraulic conductivity, all physical properties show an important dependence to the confining pressure. In particular, electrical resistivity reaches an asymptote at low confining pressures. Using the measured P wave velocities and effective medium theories, the microcrack density (ρ) and its evolution with confining pressure are estimated. For the three rocks, the microcrack density at which electrical resistivity reaches a plateau is of ρ ~0.13. This value corresponds to the threshold for crack percolation in media containing microcracks exclusively. This suggests that in porous and microcracked rocks, electrical resistivity is controlled by two independent hydraulic pathways of tubes and cracks acting in parallel. In contrast, this percolation threshold is not observed in the permeability data. A simple conceptual model is finally introduced that explains the fundamental differences between transport properties.

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“…Experiments were performed on Aji granite, also used by Watanabe and Higuchi (2015) and Sawayama and Katayama (2016). Microscopic observations indicate that the granite is composed mainly of quartz, plagioclase, K-feldspar, and biotite, with a mean grain size of 0.5 mm.…”

Section: Experimental Materials and Methodsmentioning

confidence: 99%

Fluid‐Induced Fracturing of Initially Damaged Granite Triggered by Pore Pressure Buildup

Katayama

Nicolas

Schubnel

2018

Geophysical Research Letters

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Fluid flow‐induced seismic activity has been observed in various environments; however, the relations among fluid migration, pore pressure buildup, and fracturing remain poorly understood. In the present study, we conducted fluid‐induced fracture experiments on initially damaged granite. Acoustic events and macroscopic failure of the samples were triggered exclusively by a buildup of pore pressure, and fracturing occurred when the average effective stress reached a critical stress state (following the Mohr‐Coulomb criterion). The spatiotemporal distribution of acoustic events is mainly controlled by the pore pressure diffusion front through the sample. Fluid migration velocity was dependent primarily on the initial stress state and permeability. Although the propagation of acoustic events was slower in our laboratory experiments than in natural seismic swarms, a similar parabolic relationship in space and time suggests that these microearthquakes are likely triggered by the passage of a critical pore fluid pressure through the damaged zones.

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Simultaneous measurements of elastic wave velocities and electrical conductivity in a brine-saturated granitic rock under confining pressures and their implication for interpretation of geophysical observations

Cited by 26 publications

References 26 publications

Evolution of Elastic Wave Velocities and Amplitudes During Triaxial Deformation of Aji Granite Under Dry and Water‐Saturated Conditions

Evolution of Elastic Wave Velocities and Amplitudes During Triaxial Deformation of Aji Granite Under Dry and Water‐Saturated Conditions

Pressure‐Dependent Elastic and Transport Properties of Porous and Permeable Rocks: Microstructural Control

Fluid‐Induced Fracturing of Initially Damaged Granite Triggered by Pore Pressure Buildup

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