Low Frequency Measurements of the Elastic and Anelastic Properties of the Sandstone Flooded with Supercritical CO2

Abstract

The results of the first low frequency experiments conducted on a sandstone sample (Donnybrook, Western Australia) flooded with supercritical CO2 (scCO2) are presented. The aim of the experiments was to investigate the effects of scCO2 injection on the elastic and anelastic properties of the rock. The sandstone sample (porosity – 11.4%, permeability – 0.28 mD) was cut in the direction orthogonal to a formation bedding plane and tested in a Hoek's triaxial pressure cell equipped with the means for independent control of pore and confining pressures. The pore and confining pressures were set up at 10 and 31 MPa correspondingly. The low-frequency system and the pump comprising scCO2 were held at a temperature of 42º C. Supercritical CO2 was injected into the sample preliminary saturated with distilled water. The elastic parameters obtained for the sample with scCO2 at frequencies from 0.1 to 100 Hz are very close to those for the dry sample. Some discrepancy in calculated acoustic velocities are caused by the difference in water and scCO2 densities. The extensional attenuations determined in water saturated and in flooded with scCO2 sample are practically identical. The applicability of Gassmann theory for interpretation of the experiments with supercritical CO2 was confirmed.