Experimental and Theoretical Studies of Flocculated Asphaltene Deposition from Oil in Porous Media

Abstract

Formation damage due to asphaltene deposition in oil reservoir is an issue for many countries that can have strong effect on oil production during heavy oil recovery, miscible flooding, and even primary recovery. Many tests were performed by researchers to determine the amount of deposition and reduction of permeability but the boundaries in which the asphaltene deposited in oil or at the pore surface are not determined.In this paper, series of tests are performed in order to determine the effect of asphaltene deposition on sandstone rock. Assuming negligible change of viscosity due to various concentrations of asphaltene added, results of laboratory tests performed using pre-separated asphaltene contents from crude oil are showed, to be sure that the first stage (if we divide it into precipitation from liquid phase and deposition on pore surface) of depositing is passed, n-hexane used to flocculate asphaltene particles. To generate reliable data on formation permeability damage due to asphaltene deposition, several dynamic displacement experiments with oil asphaltene content were conducted in various rates and concentrations.These laboratory tests have shown evidence of core damage happening under dynamic flowing conditions. Data were plotted in order to determine the effect of permeability reduction with comparison to reference oil permeability. It shows a significant permeability reduction after flooding. The results have shown that removal and deposition processes occurred simultaneously and trends were similar to previous works where they follow a straight-line pattern except where removal occurs. The previous available models on CMG roughly matched the data.The test results and data can be used in formation damage due to asphaltene deposition models for matching and checking models available in literature and commercial softwares.

Study of Asphaltene Precipitation and Deposition Phenomenon during WAG Application

“…In the cases of organic deposition, the damage area is normally restricted to the wellbore zone, but in the case of asphaltene precipitation the damage in oil reservoirs, is due to the region of asphaltene deposition that extends over large distances from the wellbore. porosity reduction, absolute permeability reduction, alteration of rock wettability from water-wet to oil-wet and plugging of the wellbore and piping in production facilities [19,22,27,46]. The flocculated asphaltene particles in the oil phase combine and form larger particles; these aggregates cannot pass through the pore throats and are captured inside or adhered to rock pores and grow as a separate bulk phase.…”

“…The reasons for the asphaltenes deposition can be many factors including variations of temperature, pressure, pH, composition, flow regime, wall effect and electro kinetic phenomena [3,4]. Once the asphaltene deposition occurs, it causes severe permeability and porosity reduction and wettability alteration, changing relative permeability in the reservoir and, in the severe cases plugging the wellbore and surface facilities [4,[19][20][21][22][23][24][25][26][27][28][29]. Formation damage due to asphaltene deposition in the oil industry is an issue for many fields that cause reduction in production and shutting of some of the wells and a severe detrimental effect on the economics of oil recovery [1][2][3].…”