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

Asphaltene precipitation and subsequent formation damage during oil pr oduction remains a serious problem in oil production. Asphaltenes are also of concern in petroleum processing. In this work, asphaltene prec ipitation in dense gas processes has been examined using continuous su percritical fluid extraction experiments. Experiments were performed o n 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 dat a indicated that as the cosolubilizing lighter components of the oil a re extracted, more of the heavier compounds precipitate in the pentane -insolubles test, thus showing an increase in the asphaltene content o f the residual fractions. The polar-to-nonpolar compounds ratio also i ncreased for the residual fractions relative to the original bitumen. This indicates that asphaltenes, defined as pentane-insolubles, are no t a definite compound class but are specific to a given mixture. The s tudy also indicated that it may be inappropriate to perform 'asphalten e' balances on different fractions of crude oils and bitumens since th e solubility and precipitation characteristics of the mixtures change with composition. The asphaltene content of the original oil may not b e an appropriate index in order to define the precipitation characteri stics since this is not the only fraction susceptible to precipitate i n a dense gas flooding process.