Performance of Secondary Carbonated Water Injection in Light Oil Systems

In this study, the performance of secondary carbonated water injection (CWI) was investigated at various operating pressures (i.e., P = 0.7-10.3 MPa). Prior to CWI tests, CO2 solubility in both brine and oil samples was measured using a high pressure visual cell. Next, through a series of flooding experiments, the effect of various operating conditions on the efficiency of CWI as a means of secondary oil recovery technique was investigated. Results showed that the ultimate oil recovery of secondary CWI can be increased by about 19% as compared to that of conventional water flooding (WF). It was also observed that in secondary CWI mode, an increase in operating pressure enhances the oil recovery, which is mainly attributed to higher CO2 solubility in the injected brine. It was also found that the recovery factor (RF) substantially increases to the pressure of P = 5.9 MPa followed by slow growth until the pressure reaches P = 10.3 MPa. The same turning point of P = 5.9 MPa was also observed in the plot of CO2 solubility in brine versus the operating pressure. Therefore, it was concluded that the value of CO2 solubility in brine controls the efficiency of CWI process. Additionally, less recovery factor was obtained when temperature was increased from T = 25 to 40 degrees C. The same impact was observed when the carbonation level of the injected brine was reduced from CL = 100% to CL = 50%. However, it was seen that the carbonated water (CW) injection rate minimally affect the efficiency of the CWI. From the CO2 storage point of view, the amount of CO2 that was stored at the end of secondary CWI for different operating pressures was determined, and the values ranged from 23% to 36% of total injected CO2. Thus, it was concluded that CWI considerably has great potential to permanently store the injected CO2 while significantly improving oil recovery in light oil systems.