AN EXPERIMENTAL-STUDY OF THE EFFECT OF PARAFFINIC SOLVENTS ON THE ONSET AND BULK PRECIPITATION OF ASPHALTENES

Asphaltene onset concentration and bulk deposition were measured for a typical live reservoir oil titrated with n-C6H14, n-CH(5)G(12), n-C4H 10, C3H8 C2H6, CH4 and CO2 at 100 degrees C (212 degrees F) and 29.9 M Pa (4340 psia). The concentration of titrant at asphaltene onset was o bserved to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH4 did not induce any asp haltene precipitation. Bulk deposition experiments were performed usin g a solvent:oil volume ratio of 10:1; the results indicated that the w eight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importan tly, the asphaltene molecular weight showed a maximum for n-C4H10 prec ipitated asphaltenes. Possible explanations for this unusual result ar e presented.