Improved CO₂-Foam Properties and Flow Behavior by Hydrophobically Modified Polymers: Implications for Enhanced CO₂ Storage and Oil Recovery

CO₂-foam enhanced oil recovery (EOR) has been considered a proven technology to mitigate adverse effects from CO₂ front instabilities in highly heterogeneous reservoirs, such as viscous fingering, gravity segregation, and superior flow in high permeability streaks, leading to premature CO₂ breakthrough. A highly stable CO₂-foam is required to provide significant mobility control effect that stimulates flow diversion from high-permeability to low-permeability regions, hence improved sweep efficiency. CO₂foam EOR process can also be advanced for effective CO₂ utilization and long-term CO₂ sequestration in addition to improved oil production. However, harsh in-situ environments of hydrocarbon reservoirs greatly determine the performance of CO₂-foam and the efficiency of the entire operations, leading to a need of foam formulation optimization in addition to technical development. As an innovative solution, hydrophobically modified polymer was employed to improve overall CO₂-foam properties and CO₂ mobility control performance inside porous media. A comprehensive evaluation on foaming properties (foamability and foam stability) and foam rheological behavior was performed under supercritical conditions to warrant the suitability of developed formulation as high-performance foaming agent. CO₂-foam was generated using the primary foaming agent (alpha olefin sulfonate and betaine) in combination with different types of hydrophobically modified polymers, referred as to HMP, and conventional polymers (HPAMs) as foam stabilizers. The steady-state foam resistance established by each foam during dynamic flow tests was assessed under reservoir conditions to indicate the extent of mobility control effect for better sweep efficiency and the capability of the developed CO₂-foam formulation of suppressing CO₂ migration, hence improved storage efficiency. The formulation containing the selected HMP offered an acceptable foam generation ability compared to the formulations containing classical HPAM polymers. The presence of HMP with a higher degree of hydrophobes and lower molecular weight in surfactant-stabilized foam system was able to produce an improved flow resistance. These are attributed to the formation of organized and bridged polymer network triggered by hydrophobic association in the bulk and lamella interface hence providing steric forces at the interface that leads to substantial elasticity. Results from dynamic flow experiments revealed the superior performance of HMP stabilized CO₂-foam in porous media in which its flow resistance was found to be 70% and 95% higher than that of polymer-free CO₂-foam, and individual CO₂, respectively. This research provides an alternative solution by promoting a relatively new foam formulation which is stabilized by hydrophobically modified water-soluble polymer. Besides offering better mobility control effect during EOR process, the application of developed CO₂-foam formulation was also extended to CO₂ trapping improvement for better CO₂ sequestration by suppressing unfavorable CO₂ mobility through high-permeability pathways. Therefore, the designed foam should be able to control CO₂ plumes migration, enhance CO₂ storage potential, and improve CO₂ utilization for complex reservoirs.