Real-Time 3D Imaging of Neat, and Viscosified CO2 in Displacement of Brine-Saturated Porous Media

Abstract

Abstract CO2 storage in saline aquifers may contribute to a 95% share in preventing emissions to the atmosphere. The process is inefficient due to low CO2 viscosity at the subsurface conditions. Most of the injected CO2 will spread quickly at the formation top and increase the probability of leakage. This work is aimed to demonstrate improved CO2 storage in saline aquifers by effective viscosification/thickening of the sc-CO2 at very low concentrations of engineered polymers and by slug injection. We also present results from X-ray CT imaging to advance the understanding of two-phase CO2-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 saturation spatiotemporally in brine-saturated Berea sandstone cores. In neat CO2 injection, gravity override and viscous fingering result in early breakthrough and low sweep efficiency. Cumulative brine production is approximately 30% (from fraction collector) and 35% (from X-ray CT imaging) at 2 PVI. The difference between the two is attributed to the solubility of the produced water in the produced CO2 at atmospheric pressure which has been neglected in the past. We show that when the forgotten effect is accounted for, there is a good agreement between direct measurements and in-situ saturation results. In the past, we have demonstrated that effectiveness of an oligomer of poly(1-decene) in displacement of brine by CO2 at a concentration of 1.5 wt.%. In this work, we show that the same polymer is effective at low concentration of 0.6 wt.%. The oligomer slows the breakthrough by 1.6 times and improves the brine production by 35% in horizontal orientation. Such a large effect is thought to be from the increase of the interfacial elasticity, based on the X-ray CT imaging of displacement experiments. We also show that there is no need for continuous injection of the oligomer. A slug of 0.3 PVI viscosified CO2 followed by neat CO2 injection has the same effectiveness as the continuous injection of the neat CO2. In this work, we also demonstrate the effectiveness of an engineered new molecule at 0.3 wt.% that may increase residual trapping by about 30%. The new molecule has much higher effectiveness than our recent molecule. The combination of mobility control and residual brine saturation reduction is expected to improve the CO2 storage in saline aquifers by effective viscosificaiton with low concentrations of oligomers.