Combined Asphaltene Aggregation and Deposition Investigation

This study discusses experimental and modeling results of asphaltene aggregation and deposition using various n-alkanes as precipitants to destabilize asphaltenes from a crude oil. The amount of asphaltenes precipitated as a function of precipitant carbon number and concentration was obtained after monitoring the slow kinetic aggregation process. A geometric population balance was used to estimate the asphaltene asphaltene collision efficiency during bulk aggregation. The results revealed that, for a fixed volume fraction of precipitant, the collision efficiency decreases with increasing precipitant carbon number, resulting in slower aggregation. The tendency for asphaltenes to deposit was measured using capillary flow experiments under similar conditions. Similar asphaltene deposition behavior was obtained when the results were normalized by the asphaltene solubility and other experimental factors. A modified aggregation model was applied to the results and revealed that the difference between the asphaltene and solution solubility parameters is a dominant predictor of asphaltene aggregation. The time required to form an initial deposit inside the capillary apparatus was also found to correlate with the difference between asphaltene and solution solubility parameters. However, the deposition rate of asphaltenes in the capillary apparatus did not correlate with the collision efficiency or solubility parameter difference, contrary to initial expectations. The results suggest that mass transport barriers in the apparatus provided sufficient resistance to deposition as to limit observable correlation between the deposition rate and collision efficiency.