A recent study published in Engineering has introduced a novel method for enhancing oil recovery (EOR) in high-water-cut mature reservoirs by using thickened supercritical CO₂ flooding. The research, conducted by a team from the China University of Petroleum, Northeast Petroleum University, and Pennsylvania State University, offers a detailed analysis of the potential for this method and its effectiveness in increasing crude oil recovery.

High-water-cut mature reservoirs, which are characterized by water cuts exceeding 90%, are crucial for maintaining China’s annual crude oil production. Despite the use of conventional water flooding and chemical methods, over 40% of crude oil remains unexploited in these reservoirs. The study focuses on the Daqing Oilfield, one of China’s largest oilfields, where significant remaining oil is concentrated in low-permeability areas and weakly swept zones. The research aims to develop an efficient technology to further enhance oil recovery in these challenging reservoir conditions.

The researchers utilized molecular dynamics simulation to design an optimal synthetic routine for a copolymer thickener. The copolymer, synthesized by modifying vinyl acetate (VAc) with maleic anhydride (MA) and styrene (St), was found to have good solubility, strong dispersion stability, and a high thickening effect in supercritical CO₂ (scCO₂). Laboratory experiments showed that a 0.2% mass concentration of the copolymer could increase the viscosity of scCO₂ by 39.4 times under conditions of 10 MPa pressure and 50 °C temperature.

The study conducted high-temperature, high-pressure oil displacement experiments to elucidate the EOR mechanism of the thickened scCO₂. The results indicated that thickened scCO₂ flooding could expand the vertical swept volume and inhibit gas channeling, leading to a 9% increase in oil recovery compared to traditional scCO₂ flooding. In a typical high-water-cut mature reservoir, increasing the scCO₂ viscosity by 50 times could enhance crude oil recovery by 23.1%.

The research also involved numerical simulations to predict the EOR effect in a pilot area of the Hei-46 block in Jilin Oilfield. The simulations demonstrated that higher scCO₂ thickening multiples led to more significant EOR effects. However, the study highlighted that there is an optimal scCO₂ thickening multiple, as excessively high viscosity could reduce the effectiveness of vertical remaining oil recovery and increase operational costs.

The findings suggest that thickened scCO₂ flooding could be a promising technology for significantly enhancing oil recovery in high-water-cut mature reservoirs. The study emphasizes the need for further research to develop cost-effective and environmentally friendly scCO₂ thickeners suitable for field-scale applications. Additionally, future work should explore the potential synergistic effects of combining thickened scCO₂ flooding with other EOR methods to maximize oil recovery efficiency.

The paper “A Novel Method for Enhancing Oil Recovery by Thickened Supercritical CO₂ Flooding in High-Water-Cut Mature Reservoirs,” is authored by Kaoping Song, Daigang Wang, Fengyuan Zhang, Hong Fu, Mingxing Bai, Hamid Emami-Meybodi. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.03.018. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.