Resolving resin aggregation in scCO2-extracted heavy oil by topology-driven molecular design

Supercritical CO 2 (scCO 2 ) extraction is a promising way for the recovery of heavy oil. However, the resulting raffinate heavy oil (RHO) often suffers from severe viscosity build-up. Herein, we aim to clarify the molecular origin of this post-extraction flowability deterioration and to develop topology-guided oil-soluble viscosity reducers for restoring RHO mobility. With advanced measurement and molecular simulation, the RHO by scCO 2 extraction has been fully characterized. Results show that scCO 2 extraction selectively removes light fractions, causing the viscosity of RHO to increase by 7.62 times at 30 °C. Molecular analyses reveal that this viscosity increase is mainly associated with strengthened resin–resin self-association, where the interaction landscape shifts from electrostatic repulsion toward dispersion-dominated attraction, leading to a compact aggregation network. Guided by this mechanism, two different oil-soluble viscosity reducers (DG-1 and DG-2) were designed and synthesized. DG-1 weakens peripheral association through localized polar adsorption, whereas DG-2, with an extended aromatic framework, penetrates more effectively into aromatic-rich aggregates and disrupts dense internal packing through enhanced dispersion interactions and reduced exchange-repulsion. As a result, DG-2 achieves 85.5 % viscosity reduction at 2.5 wt% and retains 64.77 % efficiency after thermal aging at 180 °C for 24 h. This work establishes a mechanism-to-design strategy for viscosity reduction, providing a water-free approach for improving the flowability of heavy oils.