Fractal analysis of asphaltene aggregation phenomena in live oils at elevated pressure and temperature

Abstract

In this work, high-pressure microscopy technique was used to measure the size and fractal dimension of asphaltene aggregates formed in different live oil samples at elevated pressures and temperatures. It was found that the asphaltene aggregates in live oil samples are irregular fractal-like structures with pressure−temperature-dependent fractal dimensions. By monitoring the variation of the fractal dimension and size of the asphaltene aggregates with pressure and temperature, the mechanisms responsible for asphaltene aggregation process at elevated pressures and temperatures can be well predicted. The range of fractal dimension of asphaltene aggregates in live oils is similar to that observed in classical colloidal systems. In light oil sample, depressurization process at lowest temperature (319 K) leads to the formation of large and loose aggregates, that is, porous aggregates with low fractal dimensions in the range from 1.63 to 1.72. With temperature rise, denser and more compact structures are formed with fractal dimensions varied in a narrow range of 1.90–2.01 at highest temperature of 408 K. In heavy oil sample, the fractal dimensions change in a wide range at different temperatures (1.56–1.90 at 368 K, and 1.68–1.89 at 333 K). From a practical viewpoint, the present study provides qualitative and quantitative information on the significance of pressure, temperature, and oil type on the shape/structure, and consequently density/compactness of asphaltene aggregates in live oils at pressure and temperature conditions of oil reservoirs.