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

Abstract

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. CO2-foam 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.