Influence of SARA Fractions on the Yield Stress of Heavy Oil.

The depletion of conventional oil resources has rendered heavy oil development a critical challenge in the energy sector. As a core rheological parameter of heavy oil, yield stress directly influences transportation efficiency and the optimization of oil displacement strategies. This study employs a multiscale analytical approach, integrating ultraviolet absorption spectroscopy and rheological testing, to systematically investigate the mechanisms by which saturate, aromatic, resin, and asphaltene (SARA) components in heavy oil and their interactions affect yield stress. The findings reveal distinct impacts of individual components on yield stress: Saturates monotonically reduce yield stress via solvation effects; Aromatics exhibit a peak-valley trend, increasing yield stress to a maximum within a specific content range before decreasing; Resins progressively elevate yield stress with increasing content by forming micellar systems that enhance structural strength; Asphaltenes display a U-shaped influence, initially disrupting resin-asphaltene complexes to reduce yield stress, followed by significant yield stress increases beyond a critical concentration due to the formation of three-dimensional network structures. Molecular interaction analysis demonstrates that saturates exhibit dual effects, aromatics reduce structural integrity by dispersing asphaltene aggregates, resins bind with asphaltenes through multifaceted interactions, and asphaltenesowing to their strongest polarityact as the structural core of networks. Elevated temperatures substantially weaken intercomponent interactions, leading to colloid network destabilization and widespread yield stress reduction. This research establishes a comprehensive theoretical framework bridging molecular mechanisms to macroscopic performance, providing crucial scientific insights for both theoretical advancements in heavy oil rheology and practical engineering applications.