(167b) A Conceptual QCM-Study of Formation, Aggregation, Adsorption and Deposition of Asphaltene Particles

Formation and deposition of asphaltene, considered as the heaviest and the most polarizable fraction of crude oil, can cause severe problems in oil production and extraction systems. Production companies bear huge reduction or even cessation in production and, in turn, un-avoided costs due to asphaltene precipitation, aggregation and deposition in wellbore or production tubings. To gain more and better insight into asphaltene formation in production systems, the conceptual investigation on the mechanisms of asphaltene adsorption and deposition on a solid surface is indispensable.

In this research work, the Quartz Crystal Microbalance (QCM) experimental technique was utilized to probe the kinetics of asphaltene adsorption and desorption using a gold surface electrode. To study the effects of flow conditions on the asphaltene aggregation and deposition, a novel and visual QCM dynamic flow cell was designed and constructed. It should be stated that throughout the experiments various model oil samples at different asphaltene contents were synthesized and the formation, aggregation and deposition of asphaltene particles were studied under different dynamic conditions using a high resolution camera, mounted on the top of the flow cell. The time-dependent size distribution of asphaltene aggregates inside the flow cell were also monitored throughout the experiments. The model oil samples were comprised of toluene, normal heptane and asphaltene particles, extracted from crude oils, at different concentrations ranging from 100 ppm to 1500ppm. The deposition of asphaltene particles on the gold surface was also investigated using the model oil containing n-heptane and toluene and the deposition rate constants reported for different samples at various static and dynamic conditions.

It was concluded that both asphaltene adsorption and deposition can increase with the concentration of asphaltene particles in the model oil samples. At higher injection rates, longer time was needed for the amount of asphaltene adsorbed on the surface to reach the steady state condition while this time was much shorter in the case of asphaltene deposition. It was also observed that while the asphaltene deposition can rapidly increase with the asphaltene concentration at small range of concentrations, it can decrease at higher asphaltene concentrations, mainly, due to the aggregation of asphaltene particles. In other words, at higher asphaltene concentrations the asphaltene particles tend to get aggregated and less asphaltene deposition can occur in the aggregation-dominated range of concentration.