Asphaltenes are the most complex fraction of crude oil, accounting for a number of undesirable properties such as high viscosity, wettability alteration, and precipitation from the oil leading to fouling of equipment and blockage of pipelines. Computational modelling of a crude oil holds the promise of being able to predict if an oil is likely to precipitate, or perform a wide scan of potential chemical inhibitors, using only a small amount of experimental data. Correctly modelling the structure and behaviour of asphaltenes at the molecular level is therefore key for ensuring the validity of these computational studies. Neutron total scattering data can be directly calculated from the structures observed in molecular simulation, and provides a vital experimental yardstick of these computational methods and models.
This study looked at asphaltene solutions and solids using small-angle and wide-angle scattering on Nimrod and was, for the first time, compared directly to the results of widely used molecular dynamics models. The simulation correctly predicted the form of the scattering curves, however the study highlighted areas where the modelling could be improved.
In particular, the researchers found that the size of the system a simulated needs to be increased to accurately compare the simulation outputs. Analysis of the wide-angle regime highlights the need to refine the molecular structural models of asphaltenes or modify the simulation approaches as the predicted intermolecular structure deviated significantly from experimental observations. The team are now actively pursuing methods to increase the simulation size, within computational constraints, which will allow for a much more detailed and valuable comparison to experiment.
Instrument: Nimrod
Related publication: “Predicting Asphaltene Aggregate Structure from Molecular Dynamics Simulation: Comparison to Neutron Total Scattering Data.” Energy Fuels 2019, 33, 5, 3787–3795
DOI: 10.1016/j.ces.2019.07.023
Funding: EPSRC, US National Science Foundation
Authors: TF Headen (ISIS), MP Hoepfner (The University of Utah)
