HPAM polymer enhanced foam for CO2 mobility control: A coreflooding experimental study

Foam technologies reduce CO 2 mobility, thereby enhancing sweep efficiency and potentially benefiting CO 2 storage and enhanced oil recovery (EOR). However, maintaining foam strength and stability under reservoir conditions remains challenging. This study examined whether adding hydrolyzed polyacrylamide (HPAM) polymers to a nonionic surfactant solution to create CO 2 polymer-enhanced foam (PEF) improves mobility control. Dynamic CO 2 mobility tests were conducted on four 9 cm Bentheimer short cores (BSC) and one 83 cm Berea long core (BLC), both initially saturated with 100% brine at 90 bar and 40°C. The tests included coinjections at 70% foam quality and CO 2 chase injections at flow rates of 2 and 4 ft/D to assess foam characteristics, including foam generation, strength, stability, residual mobility reduction, and propagation, by analyzing the DP measurements, mobility reduction factor (MRF), and apparent viscosity (μ app ). The DP, MRF, and μ app values during and after CO 2 PEF were higher than those of CO 2 foam, indicating that PEF achieved a greater reduction in CO 2 mobility. For example, the maximum MRF during CO 2 PEF was 11.03 and 5.59 versus CO 2 foam maxima of 1.91 and 2.07 (BSC1 and BSC2 at 2 ft/D). Moreover, pure CO 2 injection post PEF reduced the MRFs to 6.50 and 2.33 (BSC1 and BSC2 at 2 ft/D), whereas the MRF post CO 2 foam decreased below the baseline (MRF=1). Similarly, the maximum MRF value at 4 ft/D (BSC3) for CO 2 foam was 3.19, whereas CO 2 PEF flooding reached a maximum MRF of 22.79 (mean 12.48). In addition, during CO 2 injection after PEF, the MRFs ranged from 8.91 to 11.68, indicating sustained mobility control without continuous chemical injection. The improved flow resistance is attributed to increased foam viscosity and lamellar elasticity, as well as to blockage of flow paths by polymer retention. The μ app comparison from the tests at 2 and 4 ft/D demonstrated the shear-thinning behaviors of foam and PEF. At 2 ft/D in BSC1, the μ app values were 10.36 cP and 78.84 cP, whereas at 4 ft/D in BSC3, they were 9.78 cP and 67.74 cP for CO 2 foam and CO 2 PEF, respectively. This result may imply an advantage in mitigating injectivity challenges. The sectional pressure analysis of the 83 cm BLC showed greater upstream resistance and delayed downstream propagation under PEF, consistent with diversion by foam and with polymer-induced channel-blocking effects. This study shows that HPAM PEF markedly increases CO 2 mobility control compared to CO 2 foam during and after CO 2 PEF flooding.