The Experimental Study for Elimination of Asphaltene Precipitation in Porous Media in Solvent Injection Treatment: Based on the Appropriate Solvent Selection Criteria

In this study, after determining the set point of asphaltene flocculation by viscometer, 21 vol% of n-heptane and 79 vol% of crude oil were injected at 20 pore volume (PV) within three carbonate cores with a permeability of about 9 md. After precipitation of asphaltene in porous media, tetrahydrofuran (THF), chloroform (CF) and dichloromethane (DCM) solvents were injected into the cores at 4 PV to evaluate the permeability improvement. THF improved permeability by up to 70%. CF and DCM solvents restored permeability by 41% and 60%, respectively. The results of mapping and scanning electron microscopy (SEM) after injection of solvents showed that although THF improved permeability, the elements of nitrogen (N) and sulfur (S) remained in the porous media in place of the removed asphaltenes. In contrast, only small amounts of nitrogen remained with the DCM solvent. With CF, all three non-hydrocarbon polar elements – S, N and oxygen (O) – were present. Since the presence of these compounds in porous media causes more asphaltene to precipitate and form deposits, DCM is very suitable for this type of oil and rock according to the type of asphaltene.