Multiscale simulation of asphaltene deposition in pipeline flows

A novel multi-scale approach to asphaltene deposition in pipeline flows is presented. Pipelines are represented by Hematite (Fe2O3) surfaces, whereas Saturates, Aromatics, Resin and Asphaltene fractions (as provided by a SARA analysis) are used to represent a petroleum fluid. Molecular Dynamics (MD) and Dissipative Particle Dynamics (DPD) simulations are used to describe both the fluids and the fluid/surface interactions. The extent of asphaltene deposition in a pipe is calculated through a balance of adhesion (as calculated through MD simulations of the asphaltene-surface interaction) and drag (as represented by a Poiseuille flow in a shear field) forces, in a system of varying flowrates. Models and methods are validated first by different ways: interfacial tension and the hematite/asphaltene and asphaltene adsorption thickness on a glass surface. Two behaviors were found. The first one shows a clear decrease of asphaltene adsorbed thickness as the drag force increases (for Re < 4000); while for Re numbers higher than 5000 the adsorbed thickness decreases until it reaches a constant value. Thus, an increase in the flow rate allows drag forces to overcome the adsorption potential, reducing the amount of asphaltene adsorbed on the pipe, for a specific flow regime range. In addition, a clear reduction of density of adsorbed asphaltenes is promoted by the drag force. It is suggested that, under turbulent flow conditions, the drag forces allow a removal of molecules located at the external layer of the adsorbed asphaltene on the hematite surface. Drag forces would stabilize asphaltenes at the bulk fluid, since the shear rates could overcome asphaltene aggregation.