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-C4H10, C3H8 C2H6, CH4 and CO2 at 100 degrees C (212 degrees F) and 29.9 MPa (4340 psia). The concentration of titrant at asphaltene onset was observed to decrease approximately in a linear fashion with decreasing molecular weight of the paraffinic solvent; CH4 did not induce any asphaltene precipitation. Bulk deposition experiments were performed using a solvent:oil volume ratio of 10:1; the results indicated that the weight percent of asphaltenes precipitated increased exponentially with decreasing molecular weight of the paraffinic solvents. More importantly, the asphaltene molecular weight showed a maximum for n-C4H10 precipitated asphaltenes. Possible explanations for this unusual result are presented.