Evaluation of performance spectra of mono and divalent low saline brine injection in sandy-carbonates for mobilization of crude oil

Low salinity water (LSW) injection is one of the most economical methods of enhanced oil recovery (EOR) but its applicability as a waterflood was very limited. Also, its performance spectra significantly change when exposed to different rock compositions which need to be well understood. Thus, this study reports the impact of monovalent i.e., KCl and divalent i.e., CaCl₂ salts (of varying concentration: 0–1 wt%) on rock/fluid interaction and oil recovery from rocks of different compositions (sandstone and sandstone + carbonate). Interfacial tension (IFT) measurements, between brine and crude oil, suggested minimum IFT for KCl brine and CaCl₂ brine of 0.25 and 0.1 wt%, respectively. The variation in rock composition significantly affected the solution activity (via zeta potential) of KCl and CaCl2 brines, and brines exhibited maximum change in solution activity and adsorption of ions for the rock samples showing a compositional shift towards carbonate. Finally, flooding experiments were conducted wherein, initially porosity was found to be greater in sandstone (29.4%) as compared to carbonate (24.3%) rock composition. Finally, oil recovery and water cut profiles were obtained for different rock samples flooded by KCl and CaCl2 brines and compared with the ones of the conventional water flooding method. The results showed better performance of low saline brine injection which further improved when tests were performed for synthetic rock samples of pure carbonate (0% sandstone + 100% carbonate). A maximum oil recovery of 51% OOIP (original oil in place) was obtained for 100% sandstone while 100% carbonate demonstrated maximum oil recovery of 59% OOIP. Also, the impact of high temperature (90 °C) on these results was tested for promoting the role of low saline brine injection in carbonate reservoirs of complex conditions. Increasing the temperature further increased the amount of oil recovered to 61% OOIP, demonstrating the high efficacy of LSW at high temperatures.