Chemically enhanced water-alternating-gas injection for improved CO2 sweep efficiency and geological sequestration in CO2-EOR: Insights from physical experiments and molecular simulation
Pengwei Fang, Zhengming Yang, Qun Zhang, Hongwei Yu, Fei Feng, Yidi Wan, Jiangfei Wei, Yuhao Mei, Meiwen Cao
Abstract
Addressing gas channeling, limited sweep efficiency, and restricted CO 2 -oil miscibility in heterogeneous reservoirs during CO 2 -enhanced oil recovery (CO 2 -EOR) remains a critical challenge. Herein, a novel pressure-regulated, hydrophilic CO₂-responsive hydrogel-to-foam transition system is used to enhance oil recovery and synergistically facilitate geological CO₂ sequestration. By molecular engineering of a quaternary ammonium surfactant (HXA-1) with unsaturated alkyl chains and hydrophilic moieties, the system achieves ultralow oil-water interfacial tension and adaptive micellar structures, enabling in-situ gel-to-foam phase transition under CO 2 pressure. Core flooding experiments demonstrate that the Chemical-Assisted Water-Alternating-Gas (CWAG) technique forms a stable piston-like displacement front, boosting oil recovery by 16% compared to conventional WAG while achieving 91.2% plugging efficiency. In-situ visualization and molecular dynamics simulations reveal that the hydrophilic surfactant mitigates water-phase shielding and hydrophobic interactions, promoting CO 2 -oil miscibility and emulsification. Furthermore, the system exhibits dual functionality: under reservoir conditions, a 0.35 wt% HXA-1 solution absorbs twice as much CO 2 as WAG, significantly enhancing sequestration, while the dynamic phase transition enables deep conformance control in heterogeneous reservoirs. This work pioneers a multifunctional CO 2 -responsive material platform, offering transformative solutions for sustainable fossil fuel extraction and carbon capture, utilization, and storage (CCUS) technologies.