A laboratory study of attenuation and dispersion effects in glycerol-saturated Berea sandstone at seismic frequencies

Abstract

Knowledge of dispersion and attenuation in sedimentary rocks is important for understanding variations in seismic properties of reservoirs. These variations are often related to the presence of fluids in the pore space of rocks. In most sedimentary rocks saturated with fluid characterized by low mobility, which can stem either from low intrinsic permeability or from high fluid viscosity, relative motion between pore fluid and a rock skeleton makes a significant impact on acoustic wave attenuation and dispersion of the elastic moduli of rocks at seismic frequencies. But our current understanding of seismic velocity dispersion and attenuation in saturated rocks is limited due to a lack of laboratory data obtained at seismic frequencies. We present the results of the laboratory measurements of elastic and anelastic parameters of dry and glycerol saturated Berea sandstone (71 mD permeability, 19 % porosity) conducted at seismic frequencies. The experiments were performed with a low-frequency laboratory apparatus designed to measure the complex Young's moduli and extensional attenuation of rocks at seismic frequencies. The apparatus operates at confining pressures from 0 to 70 MPa and strain amplitudes from 10−8 to 10−6. The elastic moduli and extensional attenuation of dry and glycerol-saturated sandstone were measured at a differential pressure of 10 MPa at two temperatures of 23 and 31°C. Peaks of attenuation in the glycerol-saturated sample were found at frequencies of ∼0.6 Hz (23°C) and ∼1.5 Hz (31°C). Our analysis shows that the quantitative relationship between the extensional attenuation and the Young's modulus measured for the glycerol-saturated sandstone is consistent with the causality principle presented by the Kramers-Kronig relations.