Experimental study on the preparation and oil displacement performance of CO 2 thickeners

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CO2-enhanced oil recovery (CO2-EOR) faces challenges due to the low viscosity of supercritical CO2, which reduces sweep efficiency. This study aims to develop a hydrocarbon-based CO2 thickener to mitigate viscous fingering and enhance oil recovery. Poly-diethyl maleate (PDEM) was synthesized via free-radical polymerization of diethyl maleate, with benzoyl peroxide as the initiator. The solubility and thickening performance of PDEM in supercritical CO2 were systematically evaluated under specific conditions. Molecular dynamics (MD) simulations elucidated intermolecular interactions, whereas core-flooding experiments coupled with Nuclear magnetic resonance T2 spectroscopy quantified oil displacement efficiency. PDEM increased CO2 viscosity by 9–10-fold at 343 K and 25 MPa. MD simulations revealed dominant electrostatic interactions between CO2 and PDEM. Core-flooding demonstrated that thickened CO2 achieved 16.83% higher oil recovery than pure CO2 flooding, with significant mobilization of oil from small pores. This work presents a hydrocarbon-based thickener PDEM combining CO2-philic ester groups and oleophilic segments, enabling dual affinity for CO2 and oil. The integration of experimental and simulation approaches provides mechanistic insights into CO2-PDEM interactions, advancing the design of cost-effective, environmentally benign thickeners for CO2-EOR. These findings provide theoretical support for gas-driven development of low-permeability reservoirs.