Multiscale Research on Novel CO2-Responsive Plugging Agents for Enhanced Oil Recovery in Fractured Low-Permeability Reservoirs

Summary Low-permeable reservoirs usually exhibit the characteristics of complex fracture networks and strong heterogeneity, which contribute to fast breakthrough and low sweep efficiency during CO2 flooding. The existing plugging agents exhibit poor plugging performance, and their mechanisms and patterns are unclear. Based on the viscosifying ability of tertiary amine organics, this work developed a novel CO2-responsive control agent consisting of erucamide propyl dimethyl tertiary amine (EPDTA) and sodium p-toluenesulfonate (SPTS) that can generate high-viscosity gel to mitigate these challenges. This work presents the multiscale plugging and enhanced oil recovery (EOR) performance of the agent using microfluidic experiments and core experiments, and develops a deep learning model to quantify the mobilization characteristics of residual oil using microscopic visualization EOR experiment. The rheological properties of the agent under shear formation conditions were studied. The results show that the agent demonstrates outstanding shear resistance at 100℃, and the viscosity remained at 112 mPa·s. Subsequently, the plugging and EOR performance under various experimental conditions were systematically evaluated, with plugging coefficients consistently exceeding 98%, and the recovery of CO2 flooding increased by about 50%. Finally, the recognition accuracy of the developed deep learning model reaches up to 90%. CO2-responsive control agent promotes the plugging of fractures and high-permeability channels, transforming heterogeneous and mixed residual oil into dispersed residual oil, and thus improving recovery efficiency in the microscale. Additionally, the thickening mechanism of the CO2-responsive agent is a transformation from spherical micelles to worm-like micelles (WLMs), primarily due to the protonation of EPDTA after CO2 bubbling. The results of this study are expected to provide a benchmark to select the mobility control agent for CO2 flooding in fractured low-permeability reservoirs.