Polymer-Enhanced Foam Formulation Design for CO2-Sequestration and Mobility Control in Carbonate Reservoirs
Authors: Mumtaz Mudassar , Mushtaq Muhammad , Al-Shalabi Emad W. , Alameri Waleed , Karanikolos Georgios , Iglauer Stefan 
Published: November 2024

Abstract
Polymer-enhanced CO2 foam (PEF) is an emerging technology for gas mobility control and CO2 storage in geologic formations to mitigate anthropogenic emissions. The foam generated by surfactants alone is prone to film rupture and low endurance, particularly in Middle Eastern carbonates under harsh conditions of high temperature and salinity. Adding polymer to a surfactant solution can enhance foam stability, increase viscosity, and resist liquid drainage. This study presents a systematic polymer-stabilized foam formulation design and optimization. The work particularly focuses on developing foam formulations while incorporating polymer in surfactant formulation to enhance the foaming performance. Anionic surfactants, amphoteric surfactants, associative polymers, and an ATBS-based polymer were tested under high salinity brine (up to 167 kppm) and high temperature (up to 120°C) conditions. The Design of Experiment (DOE) approach was used to formulate the composition of the PEF formulation toward achieving maximum bulk foam stability. The obtained optimized formulation was verified experimentally for its bulk foam properties and further tested in coreflooding experiments using a carbonate outcrop to assess mobility reduction factor (MRF) and CO2 storage potential.
The results showed that selected surfactants, polymers, and combinations were stable at a high temperature of 120°C and a high salinity of 167 kppm; further tests were conducted at 95°C and 105 kppm salinity. The bulk foam stability results indicated that using a combination of surfactants and polymers significantly improved foam stability expressed by the foam’s half-life. To understand the impact of each component, the data was analyzed using various mixture regression models, and the cubic model fitted well with the foam half-life response. Binary-surfactant foam formulations performed better than using a single surfactant system. However, the ternary foam formulation of surfactants with polymer showed a strong interaction and a significant synergistic effect. The optimized polymer-enhanced foam formulation consists of 6201 ppm C-5, 3500 ppm SB, and 183.2 ppm SAV-10 polymer as high as 132 minutes at 95°C and atmospheric pressure. Additionally, the study revealed that polymer addition played a crucial role in enhancing foam longevity. Increasing the polymer concentration to adequate levels helps reduce foam coalescence due to high viscous resistance and strong foam films. Polymer concentration lower than the optimized levels renders foam less stable and weak. On the other hand, a higher concentration than the optimum results in faster foam collapse due to the fast liquid drainage. The coreflooding results showed that the optimized PEF formulation performed exceptionally well in reducing CO2 mobility and enhancing CO2 storage capacity under high-salinity (105 kppm), high-temperature (95°C), and high-pressure (1500 psi) conditions. The optimized PEF formulation generated strong foam in porous media; the mobility reduction factor (MRF) was recorded 50.2, showing higher foam viscosity than gas and brine during the injection. Furthermore, foam flooding with the optimized PEF resulted in a higher CO2 storage capacity of 77.1% compared to 14.8% for gas injection. Previous studies utilized random formulation methods to improve foaming performance by incorporating polymer as a foam stabilizer, neglecting to optimize foam stability requirements. This study is one of the few systematic works to design, optimize, and test the best-performing PEF formulation that can withstand harsh Middle Eastern reservoir conditions, providing in-depth mobility control and ensuring long-term CO2 sequestration.