Wettability Modification and Adsorption Characteristics of Imidazole-Based Ionic Liquid on Carbonate Rock: Implications for Enhanced Oil Recovery

Carbonate reservoirs contain a significant amount of oil and gas reserves, but the ultimate recovery of these reserves is very low because of higher wettability of the carbonate rock relative to crude oil. Surfactant flooding is the most common method employed to increase the recovery with the main mechanism of wettability alteration, which to an extent depends on the mineralogical attributes of the reservoir. Ionic liquid (IL), which acts as a surface-active chemical, was employed to investigate its potential impact on oil recovery in carbonate reservoirs. X-ray diffraction of the carbonate reservoir rock was done to determine the quantitative mineralogy of rock samples. Fourier transform infrared spectroscopy of carbonate reservoir rock samples and the crude oil sample indicated that the polar components of crude oil are adsorbed onto the surfaces making it oil wet. SARA analysis of the crude oil determined the percentage of heavier fractions (asphaltene and resins), which have a direct impact on altering the wettability toward oil-wet. Experimental investigation revealed that, imidazolium-based ILs were able to alter the wettability from oil-wet to water-wet conditions. In the presence of salt and alkali, IL worked efficiently in reducing the contact angle and altering the wettability toward more water-wet. The loss of IL by adsorption on the carbonate rock was investigated, and the Langmuir isotherm was found to be the best fit. The effect of salt had a detrimental effect on adsorption density of IL, as it increases with increasing salt concentration. On the other hand, the addition of alkali with an optimum concentration of 1.5-2% was found to reduce the adsorption of IL on the rock surface as alkali itself preferentially adsorbs on the rock.