Improved oil recovery by low salinity flooding (LSF) in sandstone reservoirs is hypothesized to be the result of a wettability change of the crude oil, brine, rock (COBR) system to a more water-wet state. The exact mechanism behind the wettability change upon lowering the ionic strength of the brine is, however, not yet fully understood. It is generally accepted that a strong low salinity effect requires the presence of clay minerals in the reservoir rock and preferably a high salinity of the formation water containing divalent cations. Still, COBR systems that obey these minimum requirements may give a highly variable response to low salinity flooding. To create enhanced understanding of the critical parameter(s) controlling the low salinity effect, crude oil, rock and brine from three different reservoir systems were varied in all possible combinations in a series of spontaneous imbibition tests. These tests show that, for the COBR systems analyzed here, the rock is the most critical parameter for a strong low salinity effect. Cross-correlation of the change in water saturation upon exposure to low salinity, ΔSw LS, with various rock parameters indicated the strongest correlation with rock zeta potentials.


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