![]()
Summary Recent studies have revealed that tuning SO4 concentration can significantly boost low-salinity waterflooding (LSWF) in carbonate reservoirs. In this study, for the first time, Cr2O7 and C6H5COO were added to low-salinity water (LSW), and their effect on enhanced oil recovery (EOR) was investigated and compared with SO4. This study aimed to primarily determine whether adding anions other than SO4 to LSW could further reduce interfacial tension (IFT) and make the carbonate surface water-wet thereby improve oil recovery. To this end, we added Cr2O7, C6H5COO, and SO4 to LSW at different concentrations and performed IFT, contact angle, and zeta potential experiments. Then, the flooding test was carried out in a calcite-coated micromodel for each anion at the optimal concentration. The results showed that the carbonate surface became water-wet and intermediate-wet as the concentrations of Cr2O7 and SO4 increased, respectively. However, the presence of C6H5COO did not alter the carbonate surface wettability (i.e., it remained oil-wet). The calcite dissolution, ion pair formation, and salting-in effect mechanisms might alter the carbonate surface wettability. Also, IFT declined with increasing each anion concentration in LSW (with the highest reduction associated with Cr2O7), but this reduction was not significant. Several mechanisms might lead to the IFT reduction, including the salting-in effect, H effect, and surface excess concentration. Regarding zeta potential tests, although raising the concentrations of Cr2O7 and SO4 could make the charge of the carbonate surface more negative, increasing the concentration of C6H5COO had little effect on altering this charge. Additionally, Cr2O7 made the oil/brine zeta potential positive, although the oil/brine surface charge became negative in the presence of C6H5COO and SO4. As for anions’ affinity, Cr2O7 and C6H5COO had the highest and the lowest affinity for the interface, respectively. Besides, the amount of oil recovery for LSW was 18.7±1.6%. Compared with LSW, LSW2S and LSW1Cr raised oil recovery by 3.6 and 14.3%, respectively. The results of this study support that Cr2O7 can be used in LSWF. Indeed, this anion (compared with SO4) helps produce more oil from carbonate reservoirs by improving the parameters that are effective in EOR.
Site News