Asphaltene and Normal Paraffin Effect on Gas-Oil Interfacial Tension During CO2 Injection into Asphaltenic Oil Reservoir

Asphaltene precipitation in oil reservoirs has been involved with numerous problems. Therefore, it is required to understand the precipitation mechanisms in detail in order to diminish the associated difficulties. There are several ways to detect asphaltene precipitation. One of these methods is vanishing interfacial tension (VIT) method. In this method by plotting the equilibrium interfacial tension (IFT) versus pressure, the asphaltene precipitation conditions can be predicted. In this study, for more accurate evaluation of asphaltene precipitation in oil reservoirs by using IFT versus pressure plots, synthetic oil solutions made up of toluene and normal paraffins are used. Solutions with different compositions of toluene and normal paraffins such as n-decane and n-heptane with and without asphaltene (extracted from crude oil) are prepared. Then, the equilibrium IFT of the solutions in the proximity of CO2 at different pressure conditions is measured. By plotting the IFT data versus pressure, the onset of asphaltene precipitation in presence of gas and the impact of different parameters on this phenomenon are investigated. Experimental results show that the presence of asphaltene in synthetic solutions changes the behavior of IFT data with pressure. For a solution of toluene and normal paraffin containing asphaltene, the IFT of the solution in presence of CO2 decreases linearly with two different slopes at low and high pressure ranges. The results confirm that the presence of normal paraffin intensifies asphaltene precipitation. The experimental results show that the higher mass fraction of asphaltene is, the higher would be the intensity of the asphaltene precipitation for the attempted mass fractions.