Chemical injection into oil reservoirs is considered as an effective enhanced oil recovery (EOR) method. Although some of the chemicals improve oil recovery, they may have side effects on reservoirs such as formation damage due to fluids incompatibility or chemical interactions with reservoir rocks and fluids. Since our previous work indicated promising results from Deep Eutectic Solvents (DESs; DES1 - choline chloride:glycerol = 1:2 and DES2 - choline chloride:urea = 1:2) on enhanced heavy oil recovery, we now examine the possible effects of these DESs on sandstone formation damage.
Core flooding tests were performed at reservoir pressure and different temperatures to measure possible permeability changes by DESs injection. To understand the mechanisms of formation damage, different measurements were performed: Critical injection rate beyond which fines migration will take place, water shock effects on formation damage, dry core weight measurements before and after each core flooding tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and computed tomography (CT) scanning studies of fresh and treated core samples.
Permeability measurements by core flooding tests showed that the water shock phenomenon caused severe damage (65% reduction in absolute permeability) when distilled water was injected after brine flooding. Both DESs showed positive effect on reducing the water shock damages at different temperatures, where DES2 was much more effective when compared with DES1. Core weight measurements confirmed that whenever permeability damages were higher, the amount of core weight increase was also high. Moreover, results of SEM and quantitative XRD showed that precipitation and deposition inside pores are the main sources of formation damage. In addition, CT-scanning images provided good comparisons between fresh and damaged cores. We observed that using DESs showed that despite the DES's solutions role in preventing severe water shock damage and stabilizing the clays, there was still some formation damage caused by re-crystallization and precipitation processes reducing the permeability of the core samples.