The potential of Vs and Vp-Vs relation for the monitoring of the change of CO2-saturation in porous sandstone

In this study, we conduct a simultaneous measurement of V-p and V-s of porous sandstone during drainage and imbibition to monitor the change of CO2 saturation (S-CO2) in porous sandstone under in situ pressure and temperature conditions. We estimate the S-CO2, from the change in V-s. The relationship between measured V-p and S-CO2 indicates two interesting results. First, we can find that V-p does not recover to pre-drainage levels after the end of the imbibition process. This unrecovered V-p is considered to be the effect of residual trapped C-O2. Second, there is a hysteresis between drainage and imbibition. Finally, we investigate the V-p-V-s, relation and find clear differences between water-saturation and irreducible water-saturation. From the V-p-V-s, relation, we also identify the un-recovered V-p-changes between drainage and imbibition. These results indicate the high-potential of monitoring the change of S-CO2 from V-p and V-s. (C) 2014 Elsevier Ltd. All rights reserved.