An Experimental Study of Acoustic Responses on the Injection of Supercritical CO₂ Into Sandstones Available to Purchase

Quantitative knowledge of the acoustic response of rock from an injection site on supercritical CO₂ saturation is crucial for understanding the feasibility of time-lapse seismic monitoring of CO₂ plum migration. A suite of shaley sandstones from the CRC-2 well, Otway Basin, Australia is tested to reveal the effects of supercritical CO₂ injection on acoustic responses. CO₂ is first injected into dry samples, flushed out with brine and then injected again into brine saturated samples. Such experimental protocol allows us to obtain acoustic velocities of the samples for the wide range of CO₂ saturations from 0 to 100%. On injection of supercritical CO₂ (scCO₂) into brine-saturated samples, they exhibit observable perturbation of ~7% of compressional velocities with the increase of CO₂ saturation form 0% to maximum (~50%). Changes of the dry samples before and after the CO₂ injection (if any) are not traceable by acoustic methods.