Ionic Liquid Application To Prevent Asphaltene Precipitation and Deposition during Water-Based EOR Techniques

In this study, systematic experiments were designed to investigate the effect of water/saline water and ionic liquid additives on asphaltene instability. The results revealed that emulsified water can lead to asphaltene precipitation up to 75.81% of the asphaltene content in the synthetic oil. The FTIR analysis illustrated that the heteroatoms in the asphaltene structure control the asphaltene precipitation at the water–oil interface. It was observed that the salinity has a dual effect on asphaltene instability so that asphaltene precipitation increases with an increase in salinity up to 20,000 ppm, whereas it decreases with a further increase in salinity. The “salting-in” and “salting-out” effects were used to describe this observation. By comparing the effects of four different salts (NaCl, Na2SO4, MgCl2, and MgSO4), it was found that Mg2+ intensifies the asphaltene instability rather than Na+, while the presence of SO4 2– hinders asphaltene precipitation in comparison to Cl–. The Hofmeister series was proposed for the first time to justify the effect of anions and cations on asphaltene instability in the presence of water. Moreover, the performance of three synthesized ionic liquids (TBAST, TBAOL, and TBACiN) to prevent asphaltene instability was investigated. The results revealed that the ionic liquids act through two mechanisms: (i) by replacing asphaltene absorbed on the water–oil interface and (ii) by transferring to the oleic phase and dispersing asphaltene molecules. The better performance of TBAST in reducing asphaltene precipitation by up to 72.7% demonstrated the key role of alkyl length in the structure of ionic liquids. Finally, the dynamic test results indicated that adding 1348 ppm TBAST to the injected saline water reduces asphaltene precipitation/deposition by 83.7% and enhances the ultimate recovery factor from 49.73 to 71.35%.