THE EFFECT OF COSOLUBILIZING LIGHTER COMPONENTS ON THE ASPHALTENE CONTENT OF HEAVY OILS

Asphaltene precipitation and subsequent formation damage during oil production remains a serious problem in oil production. Asphaltenes are also of concern in petroleum processing. In this work, asphaltene precipitation in dense gas processes has been examined using continuous supercritical fluid extraction experiments. Experiments were performed on a bitumen (ultra heavy oil) using propane as the solvent at several temperatures and pressures and the asphaltene contents of the original material and residual fractions were determined. The experimental data indicated that as the cosolubilizing lighter components of the oil are extracted, more of the heavier compounds precipitate in the pentane-insolubles test, thus showing an increase in the asphaltene content of the residual fractions. The polar-to-nonpolar compounds ratio also increased for the residual fractions relative to the original bitumen. This indicates that asphaltenes, defined as pentane-insolubles, are not a definite compound class but are specific to a given mixture. The study also indicated that it may be inappropriate to perform 'asphaltene' balances on different fractions of crude oils and bitumens since the solubility and precipitation characteristics of the mixtures change with composition. The asphaltene content of the original oil may not be an appropriate index in order to define the precipitation characteristics since this is not the only fraction susceptible to precipitate in a dense gas flooding process.