Role of ion exchange, surface complexation, and albite dissolution in low salinity water flooding in sandstone

Wettability alteration appears to be an important mechanism for low salinity water flooding, but two major challenges in predicting the low salinity effect are (1) to understand the contribution of ion exchange, surface complexation, and albite dissolution mechanisms, and (2) to quantify how the three mechanisms contribute to pH increase during low salinity water flooding. We thus modelled one-dimensional (1D) reactive transport, examining the ion exchange, surface complexation, and albite dissolution using PHREEQC, and compared with RezaeiDoust et al.'s [Energy and Fuels. 2011; 25(5):2151-62.] experimental pH profiles during low salinity water injection. We reasonably matched RezaeiDoust et al.'s experimental pH profiles. We found that ion exchange, and albite dissolution significantly contribute to pH increase, and surface complexation mechanism plays a minor role in pH increase. Our results suggest that basal charged clays (e.g., illite, smectite, chlorite) and albite are minerals to trigger pH increase which decreases the bridging number ( > -NH + > -COOCa) for basal charge clays, and also decrease the bonds ([ > AlOH2 (+)] [-COO-] + [ > Al:SiO-][-NH+] + [ > Al:SiO-][-COOCa+] + [ > Al:SiOCa+][ > [-COO-]) for edge charged clays (e.g., kaolinite). Our results provide insights to characterize the geochemical features of oil/brine/sandstone and shed light on constraining the intrinsic uncertainties of low salinity water FOR in sandstone reservoirs.