Abstract
Asphaltene content of an ultra-heavy oil was compared to the asphaltene contents of residual fractions obtained after supercritical extraction of the oil with propane. The asphaltene contents of the residual fractions were found to be significantly greater than the asphaltene content of the original oil even after prorating the values to weight percent of the original oil. This increase was believed to be due to the depletion of lighter cosolubilizing compounds from the oil. The H/C atomic ratio of the residual fractions was lower compared to the original oil, indicating that the ratio of polar to nonpolar compounds may also be important from precipitation considerations. Saturate and aromatic compounds were preferentially extracted and the ratio of asphaltenes to resins increased in the residual fractions relative to the original oil. The data demonstrated that the asphaltenes in the original oil were not the only compounds susceptible to precipitation and that a broader view of the precipitable material is necessary in order to understand the precipitation problem in oil reservoirs.
