CO2 Foam Generation and Strength in the Presence of Oil at High Pressure and Temperature

Abstract Foam is a field proven and laboratory verified technique to reduce CO2 mobility and mitigate the impacts of reservoir heterogeneity in CO2 enhanced oil recovery (EOR) and CO2 storage processes. However, foams are unstable and can breakdown in the presence oil and at elevated temperatures. Therefore, foam generation and stability must be screened at reservoir pressure/temperature and in the presence of oil. This work investigates the effect of oil and temperature on foam generation and stability at a range of foam qualities and injection velocities. Foam quality and rate scans using Bentheimer sandstone cores were conducted in the presence and absence of mineral oil (n-Decane) and a crude oil (Troll blend) at reservoir temperature (40°C and 60°C) and pressure (180 bar). The foam quality scans co-injected supercritical CO2 and nonionic foaming solution (0.1wt%) with increasing foam quality from 30% to 100% to determine the optimal foam quality. The optimal foam quality was then used in the rate scans to determine the effect of injection velocity on foam strength. Overall, foam was generated both in the presence and absence of both oils. However, both n-Decane and Troll blend crude oil had detrimental effects on foam strength with Troll crude oil reducing foam apparent viscosity by 93%, compared to a baseline scan without foaming solution. The optimal foam quality in the presence of both oils was between 60% and 70%. Foam rate scans in the absence and presence of residual oil revealed shear-thinning foam rheology, which is favorable for maintaining field-scale injectivity. In addition, foam recovered oil more efficiently (i.e. with less pore volumes injected), compared to experiments without foaming solution. Foam was generated at both 40°C and 60°C with optimal foam qualities of 70%. However, at 60°C the foam was weaker, compared to 40°C, likely related to changes in fluid properties. Few studies have used supercritical CO2 at reservoir pressure and temperature in the presence of oil. This work provides critical insights into the effect of oil and temperature on foam strength and stability at reservoir conditions, important parameters for ensuring field-scale success.