Enhanced oil recovery by spontaneous imbibition of imidazolium based ionic liquids on the carbonate reservoir

Abstract

Wettability alteration plays an important role in the enhanced oil recovery (EOR), particularly for the oil-wet carbonate reservoir in harsh environments. It is essential to alter the native oil-wet characteristics of the rock matrix into water-wet or intermediate-wet in an attempt to achieve the favorable EOR process. The rate of water imbibition can be greatly improved by altering the rock wettability and by reducing oil–water interfacial tension. This can be achieved by using smart water, surfactants, oilfield chemicals, functionalized nanoparticles, or a combination of these to enhance water imbibition and oil displacement. In this study, a suite of spontaneous imbibition tests was run and investigated the efficacy of eco-friendly imidazolium-based ionic liquids (ILs) on the oil-wet carbonate sample and evaluated their effectiveness for the enhanced oil recovery with the minimal concentration of ILs (≤500 ppm). In this, we have studied the various affecting parameters including; type of ILs, ILs concentration (0–500 ppm), aging time (0–8 weeks), and rock permeability (45 and 250 mD). Subsequently, two conventionally used surfactants (SDS and CTAB) were also screened for the same study in order to set the reference case. All these experiments were performed on the Indiana limestone core samples, and experimental condition was set as high temperature (100 °C) and high brine salinity (TDS: 240, 000 ppm) in order to represent the typical Saudi Arabian reservoir condition. Overall, it was observed that a maximum of 34% increment of oil recovery was recorded for IL case over the seawater. Whereas only 11% of increased recovery was achieved with the use of conventional surfactants than the seawater. It is also noted that the longer chain containing ILs had shown better recovery (34%) than the shorter chain containing ILs (27%). Furthermore, NMR T2 relaxation distribution and NMR T2D responses were acquired for the same study. This helps to estimate the rate of water invasion and oil recovery both qualitatively and quantitatively. NMR measurements confirm that seawater was ineffective in all the pores, however a very little recovery was contributed from the macropores. At the same time, ILs showed almost double the recovery compared to seawater, and all types of pores (micro-, meso, and macropores) contributed to the recovery. This suggests that ILs diffused in all type of pores due to their greater diffusiophoresis tendency than the seawater case. NMR T2D measurements correlated well with the gravimetric Amott cell imbibition test results in regards to oil and brine saturations and recovery at different stages of the imbibition process. Overall, this can be concluded that ILs are potentially strong EOR agent, which has the capability to increase the oil recovery at harsh reservoir conditions and it is cost-effective and more economically viable when compared to other conventional chemicals.