Laboratory measurements of elastic and anelastic parameters of dry and water-saturated sandstones with low (0.7- and 1.1-mD) and high (425-mD) permeability have been conducted at seismic frequencies (0.1 to 120 Hz). The experiments were performed with a laboratory apparatus that measures the stress-strain relationship in the linear regime. The extensional attenuation in water-saturated low-permeability sandstones exhibits prominent peaks in the seismic band, accompanied by considerable dispersion. Variations in attenuation and dispersion in the high-permeability sandstone are below the measurement error, as is the moduli dispersion in all the sandstones in dry condition. The experiments demonstrate that for low-permeability rocks, seismic frequencies do not necessarily correspond to the low-frequency limit (relaxed pore-fluid pressures) of acoustic wave dispersion.

A B S T R A C TPetrophysical properties of carbonate reservoirs are less predictable than that of siliciclastic reservoirs. One of the main reasons for this is the physical and chemical interactions of carbonate rocks with pore fluids. Such interactions can significantly change the elastic properties of the rock matrix and grains, making the applicability of Gassmann's fluid substitution procedure debatable. This study is an attempt to understand the mechanisms of fluid-rock interactions and the influence of these interactions on elastic parameters of carbonates. We performed precise indentation tests on Savonnières limestone at a microscale level under dry, distilled water, and n-Decane saturated conditions. Our experiments display softening of the rock matrix after water saturation. We have found that mainly the ooid cortices, peloid nuclei and prismatic intergranular cement are affected by water flooding. We also observed a shear modulus reduction in Savonnières limestone in an experiment performed at ultrasonic frequencies. One of the most important results obtained in our experimental study is that the Gassmann fluid substitution theory might not always be applicable to predict the elastic moduli of fluid-saturated limestones.

We present a simple procedure concerning the application of the Kramers‐Kronig relation for the validation of the laboratory measurements of the extensional attenuation and Young's modulus carried out on the solid specimens at seismic frequencies. The local approximation of the Kramers‐Kronig relationship was applied to verify the seismic‐frequency measurements conducted on four specimens: a viscoelastic polymethyl‐methacrylate (PMMA) sample, and two water‐ and one glycerol‐saturated sandstone samples. The experimental tests were performed at various axial (PMMA sample) and confining (sandstone samples) pressures. The measurements conducted on the PMMA sample and saturated sandstones revealed prominent extensional attenuation and significant dispersion of the Young's modulus. Our analysis shows that the quantitative relationship between the extensional attenuation and the Young's modulus is consistent with the causality principle presented by the Kramers‐Kronig relationship. No particular physical models implying any constraints on the physical properties of the samples are required for this validation.

The aim of this study was to investigate the effects of supercritical CO2 (scCO2) injection on the elastic and anelastic properties of sandstone at seismic and ultrasonic frequencies. We present the results of the low‐frequency and ultrasonic experiments conducted on water‐saturated sandstone (Donnybrook, Western Australia) flooded with scCO2. The sandstone was cut in the direction perpendicular to a formation bedding plane and tested in a Hoek triaxial pressure cell. During the experiments with scCO2, the low‐frequency and ultrasonic systems and the pump dispensing scCO2 were held at a temperature of 42°C. The elastic parameters obtained for the sandstone with scCO2 at seismic (0.1 Hz–100 Hz) and ultrasonic (∼0.5 MHz) frequencies are very close to those for the dry rock. The extensional attenuation was also measured at seismic frequencies for the dry, water‐saturated, and scCO2‐injected sandstones. The applicability of Gassmann's fluid substitution theory to obtained results was also tested during the experiments.