Effects of bead size and concentration of unstable asphaltenes obtained from different centrifugation techniques on asphaltene deposition in packed bed apparatus

Abstract

Asphaltenes are the heaviest and most polar fraction of petroleum crude oil. They are the collection of components that can be soluble in aromatics solvents such as benzene or toluene, but insoluble in normal alkanes, n-pentane, n-hexane, or n- heptane. Asphaltenes are a class of molecules consisted of grouped aromatic rings with alkane chains. Changing pressure, temperature, composition, and shear rate during transportation can cause precipitation and deposition, resulting in reduced reservoir productivity due to restricted flow lines, fouling and blockages in the pore spaces of the reservoir. The goal of this investigation is to assess validity of two aspects of the packed bed asphaltene deposition methodology and model. The first aspect is on the validity of diffusion coefficient used in the deposition model with respect to bead size in packed bed; the second aspect is on the relationship between the concentration of unstable asphaltenes, the method to measure this concentration, and the deposition rate. In the first part, it was observed that the deposition rate increases as the bead size decreases, as is predicted by the diffusion-limited deposition model used. In the second part, results indicate that concentration of unstable asphaltenes based on long time centrifugation of fresh oil-heptane mixture is the appropriate scalin g for asphaltene deposition rate, instead of aged oil-heptane mixtures.