Acoustic response of reservoir sandstones during injection of supercritical CO2

Abstract

We report experimental results for acoustic response measurements conducted during injection of supercriticalcarbon dioxide into a brine saturated sandstone plug. We measured P- and S-wave velocities (Vp, Vs) as a functionof effective stress and CO2 saturation in a sandstone plug. We demonstrate that Gassmann’s fluid substitutionprocedure matches the experimental results well for this sample. A 3.5% reduction of P-wave velocity after injectionof two pore volumes of CO2 into brine-saturated sample was measured. We conclude that measurement of Vp can beused to estimate CO2 saturations in rock. In addition, x-ray computer tomography (CT) images were acquired atreservoir conditions with a resolution of 33 µm, which provided more detailed information about CO2 saturationsand distributions in the rock. It is envisaged that these techniques (seismic and CT) can be combined in the future toenable a more holistic understanding of how fluid-fluid displacement processes are coupled with the acousticresponse characteristics of the rock.