Experimental evaluation of acid number effect on interfacial tension between nitrogen and mixtures of petroleum fractions including diesel fuel and gasoline at different pressures.

Crude oil is made up of very complex compounds, which are found in polar organic substances especially organic acid compounds in the majority. Although organic acid content in crude oil is low, the presence of organic acids affects the interfacial tension (IFT) in oil reservoirs thereby altering the enhancement of oil recovery using nitrogen gas (N(2)) injection. Therefore, in this study, the effects of pressure (1 to 35 bar), the percentage of aromatic compounds (0.0 to 100 vol%) in the aliphatic hydrocarbon samples and the organic acid (benzoic acid) content (0.0 to 0.8 g.L(- 1)) on IFT between a mixture of gasoline/diesel fuel and N(2) were investigated at a temperature of 298 K. IFT does not necessarily decrease as pressure increases for the sake of existence of aromatic compounds. IFT alteration for gasoline was more (about 8 dyne.cm(- 1)) than for diesel fuel (approximately 4 dyne.cm(- 1)) during pressure increased from 1 to 35 bar due to the replacement of heavy long chain aliphatic compounds instead of light aromatic matters. The effect of IFT alteration between N(2) and diesel fuel during increasing the organic acid content was little (approximately 1.5 dyne.cm(- 1)), in contrast, this effect was more noticeable for N(2)/gasoline (about 8 dyne.cm(- 1)). In addition, a reduced cubic model for estimating IFT between N(2) and petroleum fractions in terms of pressure, petroleum fraction composition and organic acid content was proposed with an average relative error of less than 2.6%.