یوسف کاظم زاده

The formation of sediments in the oil indus try is one of the mos t important problems in its various production sectors. These sediments lead to pipe plugging, increase in pipe thickness, channeling of oil flow, reduction in effective area of the pipe and consequently increase in pressure drop. Injection of miscible gas into the oil tank is one of the fas tes t growing enhanced oil recovery (EOR) methods in the world. Measuring the minimum miscibility of MMP is one of the mos t important s teps in planning a miscible gas injection project, for which several experimental and modeling methods have been proposed. One of the mos t important tools for unders tanding the phenomenon of asphaltene deposition is thermodynamic models and experimental relationships for predicting asphaltene deposition. Asphaltene deposition changes the composition of the oil components when it is next to the gas injection, which in turn causes a change in the minimum mixing pressure. Since mos t hydrocarbon mixtures contain nonpolar components, simple EoS can predict the phase behavior of a hydrocarbon mixture. However, for more complex sys tems, a more accurate EoS mus t be used. Also, MMP values decrease with increasing molecular weight in the injection gas

In this paper, the deposition of asphaltene and its relationship with water based EOR methods (including injection of low salinity water, injection of nanofluid and injection of emulsion solvents) from oil reservoirs have been investigated. Studies show that in the injection of low-salt water, all salt water intensifies the deposition of asphaltene. The same trend is observed for surface tension between crude oil and salt water (IFT). Increasing the volume of all brine in the mixture leads to increasing and decreasing asphaltene precipitation in low salinity and medium salinity, respectively. NiO, Fe3O4 and SiO2 nanoparticles are used to adsorb asphaltene and prevent its deposition. Different solvents can be used to remove asphaltene deposits. Among the emulsion solvents that are used as an alternative method to remove asphaltene deposit in porous media, emulsion (oil / water) with 70/30 ratio is the optimal solvent since removes all precipitated asphaltene.

Asphaltene precipitation in oil reservoirs has been involved with numerous problems. Therefore, it is required to understand the precipitation mechanisms in detail in order to diminish the associated difficulties. There are several ways to detect asphaltene precipitation. One of these methods is vanishing interfacial tension (VIT) method. In this method by plotting the equilibrium interfacial tension (IFT) versus pressure, the asphaltene precipitation conditions can be predicted. In this study, for more accurate evaluation of asphaltene precipitation in oil reservoirs by using IFT versus pressure plots, synthetic oil solutions made up of toluene and normal paraffins are used. Solutions with different compositions of toluene and normal paraffins such as n-decane and n heptane with and without asphaltene (extracted from crude oil) are prepared. Then, the equilibrium IFT of the solutions in the proximity of CO2 at different pressure conditions is measured. By plotting the IFT data versus pressure, the onset of asphaltene precipitation in presence of gas and the impact of different parameters on this phenomenon are investigated. Experimental results show that the presence of asphaltene in synthetic solutions changes the behavior of IFT data with pressure. For a solution of toluene and normal paraffin containing asphaltene, the IFT of the solution in presence of CO2 decreases linearly with two different slopes at low and high pressure ranges. The results confirm that the presence of normal paraffin intensifies asphaltene precipitation. The experimental results show that the higher mass fraction of asphaltene is, the higher would be the intensity of the asphaltene precipitation for the attempted mass fractions.

Iranian oil reservoirs are mainly fractured. Performance of such reservoirs could be significantly different form the conventional reservoirs. That is mainly due to some additional flow displacement mechanisms, which take place in fractured reservoir. One of these mechanisms is molecular diffusion, which could play a key role on oil production. The impact of molecular diffusion on flow displacement during gas injection for either displacement or storage purposes would be more pronounced in a fractured reservoir compared to that in a conventional reservoir. It is mainly because of different oil trapping types and huge difference between contact area of the in situ oil and the injected gas phase in these two kinds of reservoir. In this study, the process of natural gas storage in an Iranian heavy oil fractured reservoir isinvestigated. In this paper, specifically the impact of molecular diffusion on the primary oilproduction and different stages of gas storage process are studied using a commercial simulator. The results of this study show that molecular diffusion could play an important role on injection/ production rates as well as the average reservoir pressure during injection process. This impact would be more pronounced when a gas with different composition compared to that in the reservoir is used for storage purposes.