Sonic properties of rocks under confining pressure using the resonant bar technique

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Abstract
This paper presents in detail the resonant bar technique used to measureacoustic properties of materials in the sonic frequency range (≃5–20 kHz). Measurements are corrected for the effects of added mass and jacketing; extrinsic effects such as the sample diameter or the dispersion at higher frequencies can mask intrinsic properties of material and are analyzed here. When this technique is used on porous saturated media such as rocks, it is important to avoid the “Biot–Gardner–White” effect; this intrinsic effect can lead to erroneous high attenuations in unjacketed saturated samples. Experimental evidence of its occurrence on water-saturated rods is presented. Experimental results of velocity and attenuation obtained on various rock types such as limestones and sandstones show the drastic sensitivity of these measurements to effective pressure. Hertz’s theory can be applied to describe the behavior of under-consolidated sandstones. Under high confining pressure, sonic attenuation in water-saturated limestone samples is found to be very low (Q⩾100); attenuation in sandstones is always low (Q⩾50), except for some shaly sandstones.

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