Enhanced CO2 foam stabilization with fluorescent nano polymer microspheres for improved oil recovery: Insights from microscopic and macroscopic displacement studies

Abstract

CO₂ foam flooding is an effective enhanced oil recovery (EOR) technique that has been extensively studied for development of low-permeability reservoirs. However, during its application, poor foam stability often leads to severe gas channeling, resulting in lower recovery. In order to improve the foam stability, a CO₂ foam system was constructed by using fluorescent nano polymer microspheres (PARC(Flu-Ac)-5) and anionic surfactant sodium α-alkene sulfonate (AOS). The macroscopic and microscopic stability of the CO₂ foam system stabilized by PARC(Flu-Ac)-5 was investigated through its rheological properties, adsorption characteristics, and microscopic morphology. Furthermore, the sweep range of different foam systems and the stability of the foam in the channel were explored through the microscopic visualization model. Finally, the plugging and oil displacement performance of the CO₂ foam system stabilized by fluorescent nano polymer microspheres was evaluated through dynamic core flooding experiments conducted under CO₂ flooding reservoir conditions. Thus, the oil displacement mechanism of fluorescent nano polymer microspheres stabilizing CO₂ foam was revealed. The experimental results demonstrate that PARC(Flu-Ac)-5 microspheres greatly enhance the stability of CO₂ foam by adsorbing at the gas-liquid interface. It remains stable for 30 min when formed with 5 % oil content. The microspheres' distinctive elastic deformation characteristics enable their migration and subsequent plugging of the pores following foam rupture, thereby establishing a dual anti-gas channeling mechanism. The total recovery of CO₂ foam system stabilized by fluorescent nano polymer microspheres is 46.71 %. The oil displacement effect is better than that of the single AOS foam system, and the total recovery rate is increased by 12.02 %. By adsorbing at the gas-liquid interface of foam liquid film, PARC(Flu-Ac)-5, acting as a foam stabilizer, enhances both the stability and oil resistance of foam within porous media. This adsorption behavior thereby enabling the foam to maintain its integrity upon encountering crude oil and preventing foam coalescence and defoaming. Concurrently, under the Jamin effect of the foam, the foam preferentially occupies the pore space in high permeability layers, and the injected fluid is diverted toward unswept regions following the plugging of high permeability pathways. Consequently, the sweep range and the driving ability of the subsequent foam to enter the blind end are increased, and the recovery rate of crude oil is improved. This work lays a theoretical foundation for the field application of polymer microspheres stabilized CO₂ foam system.