Heavy crude oils present major challenges in transportation and front-end processing due to their extremely high viscosity and low API gravity. This work introduces an integrated experimental–statistical–mechanistic framework to evaluate the effect of four low–molecular-weight solvents—toluene, xylene, light naphtha, and n-hexane—on the rheology and density of Missan heavy crude oil using a high-speed baffled extraction unit designed to ensure uniform mixing. Bench-scale experiments were performed at solvent loadings of 4–12 wt% and temperatures of 15–45 °C, with viscosity and API gravity measured before and after dilution. Aromatic solvents (toluene) demonstrated superior upgrading performance, achieving viscosity reductions of 63.2% at 25°C and 63.4% at 35°C, and API increasing of 5.3°API at 12 wt% loading and all operating temperatures. One-way ANOVA confirmed that solvent type had a highly significant influence on both viscosity and API gravity across all temperatures (p 0.996) and linear dose–response models (VR = a + bC) captured the observed rheological behavior with high fidelity. Mechanistic analysis attributes the superior efficacy of aromatic solvents to strong π–π interactions enabling asphaltene peptization, while aliphatic solvents act primarily through dilution. The results define solvent-selection and dosage windows relevant to pipeline hydraulics and field operations, and demonstrate that optimized aromatic–aliphatic co-blends provide a tunable, low-complexity strategy for improving the flowability of Iraqi heavy crude oils.
Khamees et al. (2026) studied this question.