A new apparatus for measuring elastic wave velocity and electrical conductivity of fluid‐saturated rocks at various confining and pore‐fluid pressures

Watanabe, Tohru; Higuchi, A.

doi:10.1111/gfl.12050

Cited by 5 publications

(2 citation statements)

References 18 publications

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“…2a). A pressure vessel (Riken-Seiki, PV-2 M-S14) was equipped with a plastic The number inside brackets shows the error in the last digit piston-cylinder system, which was employed for porefluid pressure control and electrical isolation (Watanabe and Higuchi 2014). A pump for controlling pore-fluid pressure moves the piston to change the pore-fluid pressure.…”

Section: Ultrasonic Velocity and Strain Measurements On Dry Samplesmentioning

confidence: 99%

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

Higuchi

2015

Prog. in Earth and Planet. Sci.

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Simultaneous measurements of elastic wave velocity and electrical conductivity in a brine-saturated granitic rock were conducted under confining pressures of up to 180 MPa. Contrasting changes in velocity and conductivity were observed. As the confining pressure increased to 50 MPa, compressional and shear wave velocities increased by less than 10 %. On the other hand, electrical conductivity decreased by an order of magnitude. Both changes must be caused by the closure of cracks under pressures. Microstructural examinations showed that most cracks were open grain boundaries. In reality, a crack is composed of many segments with different apertures. If crack segments have a similar length, segments with small apertures are closed at low pressures to greatly reduce conductivity, while those with wide apertures are open even at high pressures. The latter must form an interconnected fluid path to maintain the electrical conduction through fluid. A power law distribution of apertures causes a steep decrease in conductivity at low pressures. An empirical relation between the crack density parameter and normalized conductivity was obtained. The normalized conductivity is the ratio of bulk conductivity to the conductivity of a pore fluid. This relation should be a basis for quantitative interpretation of observed seismic velocity and electrical conductivity.

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Section: Ultrasonic Velocity and Strain Measurements On Dry Samplesmentioning

confidence: 99%

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

Higuchi

2015

Prog. in Earth and Planet. Sci.

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“…One pump moves the piston to control the pore-fluid pressure. Watanabe and Higuchi (2014) examined the relationship between the pore-fluid and silicone oil pressures. The pore-fluid pressure in a sample can be controlled without a significant contribution of the friction between the piston and cylinder.…”

Section: Ultrasonic Velocity and Conductivity Measurements On Wet Sammentioning

confidence: 99%

Elastic wave velocity and electrical conductivity in a brine-saturated rock and microstructure of pores

Watanabe

Makimura

Kaiwa

et al. 2019

Earth Planets Space

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Elastic wave velocity and electrical conductivity in a brine-saturated granitic rock were measured under confining pressures of up to 150 MPa and microstructure of pores was examined with SEM on ion-milled surfaces to understand the pores that govern electrical conduction at high pressures. The closure of cracks under pressure causes the increase in velocity and decrease in conductivity. Conductivity decreases steeply below 10 MPa and then gradually at higher pressures. Though cracks are mostly closed at the confining pressure of 150 MPa, brine must be still interconnected to show observed conductivity. SEM observation shows that some cracks have remarkable variation in aperture. The aperture varies from ~ 100 nm to ~ 3 μm along a crack. FIB-SEM observation suggests that wide aperture parts are interconnected in a crack. Both wide and narrow aperture parts work parallel as conduction paths at low pressures. At high pressures, narrow aperture parts are closed but wide aperture parts are still open to maintain conduction paths. The closure of narrow aperture parts leads to a steep decrease in conductivity, since narrow aperture parts dominate cracks. There should be cracks in various sizes in the crust: from grain boundaries to large faults. A crack must have a variation in aperture, and wide aperture parts must govern the conduction paths at depths. A simple tube model was employed to estimate the fluid volume fraction. The fluid volume fraction of 10 −4-10 −3 is estimated for the conductivity of 10 −2 S/m. Conduction paths composed of wide aperture parts are consistent with observed moderate fluctuations (< 10%) in seismic velocity in the crust.

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Geometry and spatial variations of seismic reflection intensity of the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

et al. 2017

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A new apparatus for measuring elastic wave velocity and electrical conductivity of fluid‐saturated rocks at various confining and pore‐fluid pressures

Cited by 5 publications

References 18 publications

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

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

Elastic wave velocity and electrical conductivity in a brine-saturated rock and microstructure of pores

Geometry and spatial variations of seismic reflection intensity of the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

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