Colloidal Properties of Crude Oils Studied by Dynamic Light-Scattering

Colloidal properties and kinetics of asphaltene aggregation in three crude oils using a dynamic light-scattering method adapted to opaque fluids were investigated. The technique makes it possible to measure the size of particles suspended in nearly nontransparent liquid media. The studied native crude oils were found to have persisting colloidal particles. The observed particles are assumed to be asphaltene/resin aggregates. Using n-heptane as a precipitant, asphaltene aggregation kinetics in crude oils was studied. Experimental measurements of the particle size as a function of time in solutions with different oil/precipitant ratios are reported. The aggregation kinetics accelerates with increasing precipitant concentration. The oil sample with a large amount of paraffins is on the edge of instability and exhibits a slow asphaltene aggregation process without precipitant. Aggregation in the two other oils starts only at some threshold concentration of the precipitant, lasts a short time, and results in the formation of stable-in-size particles. The results obtained prove that dynamic light scattering is an effective method to test petroleum colloid stability.