Investigation of Effects of Frequency and n-heptane on Rheological Behavior of Crude Oil – A Case Study of Mansouri Reservoir

Asphaltene not only increases the viscosity of crude oil, but it can block oil extraction, transportation, and separation equipment. In the present study, effects of frequency and addition of n-heptane on rheological behavior of two oil samples (i.e., 23 and 71) from Mansouri oil reservoir (Iran) are investigated. Variation of viscosity is used as a criterion for amount of asphaltene separation, and loss factor is employed for distinguish the viscos as well as elastic (liquid or gel-like) behavior of the oil samples. Both viscosity and frequency tests have been conducted at different concentrations of n-heptane. The viscosity tests revealed that addition of n-heptane to the oil samples results in separation of high amount of their asphaltene. Moreover, viscosity of the oil samples continuously decreases by increasing the concentration of n-heptane. Afterwards, the numerical values of loss factor for the oil samples having different concentrations of n-heptane are measured using the frequency test. It’s simply possible to understand liquid or gel-like behavior of oil using this factor.  Finally, by focusing on viscosity decrease as well as liquid-like behavior of oil, the optimum range for frequency and concentration of n-heptane are determined. The results revealed that by adding 75 volume percent of n-heptane to oil sample of 23 in frequency of higher than 33.6 rad.s-1, the liquid-like behavior is seen, and viscosity decreased more than 97%. Moreover, the best results for the oil sample of 71 is obtained during adding 75 volume percent of n-heptane in frequency of higher than 23.4 rad.s-1. The oil sample experiences more than 96% decrease in its viscosity, and it also shows a liquid-like behavior in this condition.