Asphaltene is the heaviest and most polar fraction of crude oil that creates many problems in various sections of petroleum industry including reservoir development, well tubing, surface facilities and pipelines. There have been many investigations of the consequences of asphaltene precipitation but the adsorption of asphaltene on rock surfaces and its impact on multiphase flow are not yet well understood.
In this work, the effects of asphaltene adsorption on wettability, relative permeability, and displacement efficiency in porous media were evaluated using flow experiments in sand-packs. Clay content and water film residing between pore surface and the hydrocarbon phase are recognized as the governing factors on the level of adsorption. These experiments involved pre- and post-adsorption measurements of relative permeability and recovery in sand packs. Adsorption on sand particles was induced and measured by extended injection of asphaltene solution with known concentration into the sand pack and collection of effluent samples for analysis. A spectrophotometer was employed to measure the asphaltene concentration of each sample and the dynamic adsorption curves were obtained by the subsequent material balance calculations. Adsorption reversibility was examined by analyzing the sand samples at different sections of sand-pack and the wettability alternation was inferred from the displacement behavior. Observed improvement in the displacement behavior is explained by the combined effects of desorption due to brine injection in the post adsorption waterflood and by reduction of interfacial tension due to surface active properties of asphaltene particles.
The experimental results show the importance of the existence and properties of water film on the extent of asphaltene adsorption. Presence of clay intensifies the adsorption phenomenon but its impact on two phase flow behavior and recovery depends on the brine salinity. Maximum adsorption occurred under direct contact of sand surface and asphaltene solution when no water film was present, which resulted in more oil-wet conditions, thereby reducing the relative permeability to asphaltene solution and recovery.