Evaluating physicochemical properties of crude oil as indicators of low-salinity–induced wettability alteration in carbonate minerals

Abstract

the injection of low-salinity brine enhances oil recovery by altering the mineral wettability in carbonate reservoirs. However, the reported effectiveness of low-salinity water varies significantly in the literature, and the underlying mechanism of wettability alteration is controversial. In this work, we investigate the relationships between characteristics of crude oils and the oils' response to low-salinity water in a spontaneous imbibition test, aiming (1) to identify suitable indicators of the effectiveness of low-salinity water and (2) to evaluate possible mechanisms of low-salinity-induced wettability alteration, including rock/oil charge repulsion and microdispersion formation. Seven oils are tested by spontaneous imbibition and fully characterized in terms of their acidity, zeta potential, interfacial tension, microdispersion propensity, water-soluble organics content and saturate-aromatic-resinasphaltene fractionation. For the first time, the effectiveness of low-salinity water is found to positively correlate with the oil interfacial tension in low-salinity water. Oils with higher interfacial activity are found to respond more positively to low-salinity water. Moreover, cryogenic transmission electron microscopy images suggest that microdispersion is essentially macroemulsion, and its formation is an effective indicator-but not the root cause-of wettability alteration. The repulsive zeta potential for the rock and the oil in low-salinity water is found to be an insufficient condition for wettability alteration in carbonate minerals.

Relevance of zeta potential as a tool for predicting the response of controlled salinity waterflooding in oil–water-carbonate systems

“…Many inconsistencies are then obtained when comparing the two methods. According to other studies, the oil/water interface generally exhibits a more negative value than the rock/water interface, especially in low salinity conditions [15,42,59,63,64], which is in agreement with our results using EPM.…”

“…Also, they observed one specific case where it was not possible to correctly predict the response, which questions a possible causal relationship between electrostatic repulsion and additional oil recovery. An absence of clear correlation has also been observed by other authors [42,43]. Hence, interpretation must be done case by case to determine the efficiency of CSW on the COBR system under consideration.…”

“…Firstly, even if the sign of the macroscopic zeta potential can be defined, it only provides a weighted average of the charge at the shear plane. This value does not reflect the abundance of positive and negative surface sites in carbonates [42,60], and many sites can still have an opposite polarity as the one of zeta potential. As a result, the conclusion that electrostatic repulsion is expected due to the same polarity for rock/water and oil/water interfaces may only be valid for some sites and is not generalizable to the entire rock.…”

Investigation of crude oil properties impact on wettability alteration during low salinity water flooding using an improved geochemical model

“…Carbonate reservoirs contain a substantial amount of the world’s oil reserves 1 , but unfortunately, their recoveries are not as high as enough 2 . Laboratory experiments and field trials have shown that enhanced oil recovery from carbonate reservoirs can be obtained by modifying the injected brine composition in a process called low-salinity water flooding (LSWF) 3 , 4 .…”

Novel Approach to Study the Impact of Asphaltene Properties on Low Salinity Flooding

“…Details of group density, monomeric vs. polymeric, or structure, short vs. long chains, are concealed in these numbers. Correlating the magnitudes of both numbers with wettability has been investigated for a long time, e.g., Dubey and Doe (1993); Farooq et al 2019; Song et al (2020). Some researchers have tried to vary the values of both numbers or the ratio between the numbers to be correlated with recovery (Puntervold et al, 2007).…”