Spatiotemporal X- Ray Imaging of Neat and Viscosified CO2 in Displacement of Brine- Saturated Porous Media

CO2 2 storage in saline aquifers may contribute to a 90% share in preventing emissions to the atmosphere. Due to low CO2 2 viscosity at the subsurface often found in supercritical (sc) conditions, the injected CO2 2 may spread quickly at the formation top and increase the probability of leakage. This work relates to improved CO2 2 storage in saline aquifers by effective viscosification of the sc- CO2 2 at very low concentrations of engineered oligomers and the effectiveness of slug injection of viscosified CO2 2 (vis- CO2). 2 ). We present the results from X- ray computed tomography (CT) imaging to advance the understanding of two- phase CO2- brine 2- brine flow in porous media and firmly establish the transport mechanisms. X- ray CT imaging of displacement experiments is conducted to quantify the in- situ sc- CO2 2 saturation spatiotemporally. In neat CO2 2 injection, gravity override and adverse mobility ratio may result in early breakthrough and low sweep efficiency. We find cumulative brine production from the fraction collector to be lower than X- ray CT imaging at 2 pore volume (PV) injection. The difference between the two is attributed to the solubility of the produced water in the produced CO2 2 at atmospheric pressure. We show that when the solubility is accounted for, there is a good agreement between direct measurements and in- situ saturation results. There are three reports (two by the same group) that oligomers of 1- decene (O1D) with six repeat units may have marginal CO2 2 viscosification. The majority of published work by other groups shows that O1D with six repeat units and higher are effective CO2 2 viscosifiers. In the past, we have demonstrated the effectiveness of an O1D in the displacement of brine by CO2 2 at a concentration of 1.5 wt%. The effectiveness is examined and identified by three different methods. In this work, we show that the same oligomer is effective at a low concentration of 0.6 wt%. The oligomer slows the breakthrough by 1.6 times and improves the brine production by 34% in the horizontal orientation. X- ray CT imaging results reveal that such a large effect may be from the increase in the interfacial elasticity. We also show that there is no need for continuous injection of the oligomer. A slug of 0.3 PV injection (PVI) of vis- CO2 2 followed by neat CO2 2 injection has the same effectiveness as the continuous injection of the vis- CO2. 2 . In this work, we also demonstrate the effectiveness of a new engineered molecule at 0.3 wt% that may increase residual trapping by about 35%. The combination of mobility control and residual brine saturation reduction is expected to improve CO2 2 storage by effective viscosification with low concentrations of oligomers.