Abstract
While numerous investigations have studied asphaltene precipitation and deposition in porous media and their effects on absolute permeability, there is still a knowledge gap for understanding the changes in two-phase flow behaviour, displacement performance, relative permeability and recovery due to asphaltene adsorption and wettability alternation. The objectives of this work are: 1) to study the effect of brine salinity and asphaltene concentration on adsorption of asphaltene on pore surfaces and 2) to evaluate the effect of asphaltene adsorption on waterflooding performance and oil-water relative permeability. Experiments were conducted in sand-packs and each sand-pack was subjected to a series of flow tests comprising: 1) measurement of absolute permeability, 2) injection of pure toluene to displace the brine down to irreducible water saturation, 3) waterflooding at a constant rate to determine oil-water relative permeability, 4) long-term injection of a solution of asphaltene in toluene to allow the asphaltene to adsorb on sand surfaces and 5) a second waterflood to evaluate the post adsorption performance of waterflooding and oil-water relative permeability. Effluent samples were collected during the injection of asphaltene solution and analyzed with a spectro-photometric technique to determine the asphaltene concentration. The level of adsorption was determined from asphaltene material balance. A back pressure regulator was used to maintain the pressure of the system and the pressure drop across the sand-pack was measured and recorded. Furthermore, the interfacial tensions between asphaltene solutions and brines of different concentration were measured. A history-matching technique was developed to determine the shape of relative permeability curves by matching the production data using a genetic algorithm. The experimental results show that relative permeability and oil recovery were affected by asphaltene adsorption. The effect was more pronounced when the brine salinity was low. Displacement performance and recovery strongly depend on rock-fluid properties which may be affected by asphaltene adsorption.
