Different models have been proposed for deposition of asphaltene on reservoir rocks that due to complexity of asphaltene nature, most of them have not been productive. Here, a reliable model is proposed which despite of previous models, considers the change in asphaltene saturation in the core. The obtained experimental data in the laboratory was used for model validation. In this work, a series of core flooding tests was carried out in presence of connate water at different solvent-oil volume ratios. Pressure drop was measured at three different terminals along the core. The obtained experimental data as well as mass balance equations, momentum equation, asphaltene deposition and permeability reduction models were employed in an iterative scheme to simulate the deposition process. Genetic algorithm (GA), which is a powerful tool, was applied for history matching, optimization and determination of the model parameters. Well match observed between the model results and experimental data confirms the accuracy of the proposed mathematical model of asphaltene deposition in porous media. Also, applied improvement on the model resulted in accurate simulation as well as determination of precipitated asphaltene saturation. Optimization shows that all deposition mechanisms, surface deposition, entrainment and pore plugging, are dominant during the permeability evolution process. Results of this work can be helpful for reliable simulation of the dynamic asphaltene deposition process during different production schemes.

No abstract

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.

No abstract

Different models have been proposed for deposition of asphaltene on reservoir rocks that due to complexity of asphaltene nature, most of them have not been productive. Here, a reliable model is proposed which despite of previous models, considers the change in asphaltene saturation in the core. The obtained experimental data in the laboratory was used for model validation. In this work, a series of core flooding tests was carried out in presence of connate water at different solvent-oil volume ratios. Pressure drop was measured at three different terminals along the core. The obtained experimental data as well as mass balance equations, momentum equation, asphaltene deposition and permeability reduction models were employed in an iterative scheme to simulate the deposition process. Genetic algorithm (GA), which is a powerful tool, was applied for history matching, optimization and determination of the model parameters. Well match observed between the model results and experimental data confirms the accuracy of the proposed mathematical model of asphaltene deposition in porous media. Also, applied improvement on the model resulted in accurate simulation as well as determination of precipitated asphaltene saturation. Optimization shows that all deposition mechanisms, surface deposition, entrainment and pore plugging, are dominant during the permeability evolution process. Results of this work can be helpful for reliable simulation of the dynamic asphaltene deposition process during different production schemes.