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

Abstract

This paper presents in detail the resonant bar technique used to measure acoustic 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.

Experimental studies on perturbed acoustic resonant spectroscopy by a small rock sample in a cylindrical cavity

“…The resonant-bar method is a typical resonant method based on the measured resonant frequency and the bandwidth of frequency spectrum of rock bar with regular configuration to calculate the velocity and the quality factor of the measurement samples. This method is also widely used in measurements of elastic parameters and nonlinear properties of a rock sample [11][12][13][14][15] . The merit of this method is that the measurement can be made at a frequency as low as several kHz or even lower if a longer rock sample is used.…”

Influence of change in physical state on elastic nonlinear response in rock: Significance of effective pressure and water saturation

“…We compare three very different rock types: A clean quartz sandstone (Fontainebleau sandstone), a sandstone containing clay (Meule sandstone), and a peletoidal limestone (Lavoux limestone) [Lucet et al, 1991]. Pressure and water saturation results were 'compared to results obtained from two relatively elastically linear, intact standards: polycarbonate and Pyrex glass.…”

Propagation des ondes élastiques dans les matériaux non linéaires Aperçu des résultats de laboratoire obtenus sur les roches et des applications possibles en géophysique

“…On pourra trouver dans Johnson et Rasolofosaon (1996b) Lucet et al, 1991, pour une prŽsentation extensive de la rŽsonance linŽaire), dans laquelle on augmente l'excitation jusqu'ˆ atteindre des valeurs de dŽformation supŽrieures ˆ 10 Ð5 (voir par exemple, Bulau et al, 1984). Rappelons le principe de l'expŽ-rience de barre rŽsonnante : une barre de roche est mise en rŽsonance par une excitation sinuso•dale d'une de ses extrŽmitŽs (syst•me aimant/bobine par exemple), tandis que la vibration rŽsultante (A) est mesurŽe ˆ l'autre extrŽmitŽ (par un accŽlŽrom•tre par exemple).…”