Experimental study on seismic response during CO2 sequestration with different phase state

• Phase transition of CO2 in porous media is detected by ultrasonic method (not ART).
• Integration of ultrasonic sensors & ports of core holder to obtain better signal.
• Conjoint analysis of Vp and amplitude of brine or CO2 saturated sandstones.
• We examine the effect of porosity to the phase transition of CO2 in porous media.
• We examine the location of CO2 in phase diagram to the phase transition of CO2.

Geological CO2 sequestration is one of the most promising methods for reducing anthropogenic CO2 emissions into the atmosphere. Saline aquifers, coal beds, depleted oil and gas reservoirs are all ideal locations for greenhouse gas storage. For a sedimentary basin, CO2 can exist in gas, liquid or supercritical fluid phase state. It will cause totally different response for the seismic waves where seismic methods are widely used for sequestration monitoring. To better understand the phase transition effect, ultrasonic experiments were conducted in 6 natural cores with fully saturated brine and CO2, respectively. Due to the significant difference in compressibility, the obvious inflexions for both P-wave velocity and amplitude were concluded to be caused by the phase transitions. In addition, an increase in dew point pressure of CO2 in porous media was observed. Temperature and rock porosity are two key factors which dominates these changes.