Energy & Fuels, Vol.27, No.2, 622-639, 2013
Asphaltene Deposition under Dynamic Conditions Theoretical and Experimental Investigation
In this work, a new model based on the multilayer adsorption kinetic mechanism and four material balance equations for oil, asphaltene, gas, and water phase has been developed to account for asphaltene deposition in porous media under dynamic conditions and the model was verified using experimental data obtained in this work and also with those reported in the literature. The results showed that the developed model based on multilayer adsorption kinetic mechanism can correlate more accurately the oil flooding experimental data in comparison to the previous models based on the mechanical plugging mechanism, in particular in carbonate core samples. Also, a series of experiments was carried to determine the permeability reduction of carbonate, sandstone, and dolomite core samples due to asphaltene deposition using an Iranian bottom hole live oil sample which is close to reservoir conditions in order to study the effect of different parameters on asphaltene deposition mechanisms during dynamic conditions in porous media. The performance of the effective parameters of porous media on asphaltene deposition such as mineral composition and morphology of surface was also studied using X-ray, elemental analysis, and scanning electron micrographs (SEMs). It was found that an increase of the iron content of core sample leads to a less permeability damage and an increase of the calcium content of core sample leads to an increase of the permeability damage during natural depletion due to asphaltene deposition. SEMs of carbonate core sample showed the formation of large clusters of asphaltene with characteristic sizes that greatly exceed the monolayer deposition characteristic size. Also, a novel experimental method was designed and proposed to distinguish between the mechanical plugging and adsorption mechanisms of asphaltene using the cyclohexane or toluene reverse flooding and it has been found that 60-82% permeability reduction by asphaltene deposition was caused by mechanical plugging mechanism during a fast process, whereas 18-40% of formation damage is due to an adsorption mechanism that takes place in a longer time.