The elastic properties of rocks depend on the mineral constituents, pore structure, saturating fluids, and stress (loading) conditions. To study these properties, we measured ultrasonic P- and S-wave velocities as a function of the differential (confining minus pore) pressure and propose an unrelaxed double-porosity acoustoelasticity model, which generalizes the single-porosity one. The new approach includes the effects of crack closure, based on the David-Zimmerman model, and the squirt-flow mechanism, based on the Gurevich model. When cracks are open at low differential pressures, their properties dominate the wave velocity variations, followed by the squirt-flow mechanism. Then, a transition occurs, where cracks partially close, and the squirt-flow effect vanishes. At high pressures, cracks close and acoustoelasticity effects prevail. This behavior is observed in sedimentary rocks, whereas in granites, which have a low crack content, the acoustoelastic effect is dominant at all pressures.

Stress Effects on Wave Velocities of Rocks: Contribution of Crack Closure, Squirt Flow and Acoustoelasticity

Carcione J. M.
2022-01-01

Abstract

The elastic properties of rocks depend on the mineral constituents, pore structure, saturating fluids, and stress (loading) conditions. To study these properties, we measured ultrasonic P- and S-wave velocities as a function of the differential (confining minus pore) pressure and propose an unrelaxed double-porosity acoustoelasticity model, which generalizes the single-porosity one. The new approach includes the effects of crack closure, based on the David-Zimmerman model, and the squirt-flow mechanism, based on the Gurevich model. When cracks are open at low differential pressures, their properties dominate the wave velocity variations, followed by the squirt-flow mechanism. Then, a transition occurs, where cracks partially close, and the squirt-flow effect vanishes. At high pressures, cracks close and acoustoelasticity effects prevail. This behavior is observed in sedimentary rocks, whereas in granites, which have a low crack content, the acoustoelastic effect is dominant at all pressures.
2022
acoustic wave velocities
crack closure
squirt flow
acoustoelasticity
stress
porosity
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14083/26083
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