Experimental investigation of surfactants and their ethanol blends for CO2–oil miscibility enhancement in CO2-EOR
Shuyang Liu, Minfeng Li, Jiayu Chen, Ying Teng, Peng-Fei Wang, Junrong Liu
Abstract
As one promising CO 2 capture utilization and storage (CCUS) technology, miscible CO 2 -enhanced oil recovery (CO 2 -EOR) significantly outperforms immiscible flooding in enhancing oil production and storing CO 2 . However, achieving CO 2 miscible flooding is often hindered by the high minimum miscibility pressure of CO 2 –oil system in many reservoirs. To address this issue, this study focuses on the mechanisms for enhancing CO 2 –oil miscibility using different types of surfactants and their blends with ethanol. The effects of fatty alcohol polyoxyethylene ethers (EO), fatty alcohol polyoxypropylene ethers (PO), tributyl citrate (TC), and glyceryl triacetate (GT) on the CO 2 –oil miscibility pressure are quantitatively analyzed, as well as their synergy with ethanol. Results demonstrated that all tested surfactant additives reduce the CO 2 –oil miscibility pressure. For ether-based surfactant additives, an increase in the degree of polymerization (CO 2 -philic groups) weakens the effectiveness to reduce miscibility pressure. Oxygen atoms in the functional group contribute more significantly to miscibility enhancement than carbon atoms. Among ester surfactants, GT achieved the best reduction effect of miscibility pressure (11.82% at 3 wt%), attributed to its symmetrical short side-chain structure and ester groups. Furthermore, ethanol exhibited a significant improvement for surfactants in enhancing miscibility. Notably, the reduction of CO 2 –oil miscibility pressure increases to 27.9% by 3 wt% GT blended with 5 wt% ethanol. These findings demonstrate that blending surfactants with ethanol is a feasible and effective strategy to facilitate miscible CO 2 flooding. This study provides valuable insights and practical guidance for the field implementation of miscible CO 2 -EOR.