Modeling porous media impairment by asphaltenes caused by pressure reduction

Abstract

Porous media impairment by asphaltenes, precipitating from oil due to a pressure reduction below the onset precipitation pressure, is modeled. Two major impairment mechanisms are accounted for by a model developed. First, submicron-sized asphaltene particles, driven by Brownian motion, deposit on porous media surfaces causing a decrease in an equivalent hydraulic radius that leads to a rock permeability reduction. Second, particles agglomerate with each other and relatively large agglomerates plug pore throats contributing into the impairment process. A porous medium is represented by a set of capillary channels with permeability equal to that of real porous rock. Evolution of particle size distribution due to agglomeration is modeled by population balance approach. A process of removal of deposited asphaltenes from pores, caused by entrainment with a viscous flow, is accounted for by an empirical function. The impairment process in a long slimtube, for which experimental data are available, is modeled. The computational results are compared with the experimental ones and meticulously analyzed. A negligibly small contribution of pore plugging into total asphaltene impairment, caused by a pressure drop, is revealed. It is also concluded that only a minor fraction of deposited asphaltenes damages porous medium, whereas the vast majority is flushed away with a flow. An applicability of the model developed to simulation of cylindrical reservoir impairment by asphaltenes is also discussed.