A SMALL-ANGLE X-RAY-SCATTERING STUDY OF THE EFFECT OF PRESSURE ON THEAGGREGATION OF ASPHALTENE FRACTIONS IN PETROLEUM FLUIDS UNDER NEAR-CRITICAL SOLVENT CONDITIONS

Small angle X-ray scattering was used to determine the effect of press ure on the extent of asphaltene aggregation for a system under near-cr itical conditions. A mixture containing 60 vol % Crude Oil A in n-pent ane was studied at 110-degrees-C, at pressures ranging from 25 to 400 bar. As the pressure of the near-critical solution is isothermally dec reased, these results indicate (1) an increase in the extent of asphal tene aggregation and/or (2) increased attractive interactions among ag gregates. Information derived from different regions of the X-ray scat tering curve indicate increasing aggregation with decreasing pressure. From these experimental results, together with theoretical interpreta tion, we infer that as the pressure is reduced, increased aggregation of asphaltenes results which may contribute to formation damage in hyd rocarbon reservoirs, and to fouling in hydrotreatment and cracking cat alysts.