Influence of the cationic degree and molar mass of modified starches on their physicochemical properties and capability to enhance the oil recovery process

Polysaccharides and their derivatives are used as additives in numerous petroleum industrial processes, especially in enhanced oil recovery (EOR). There exists however, a lack of studies concerning how their physicochemical properties affect the oil recovery process. This work presents an investigation of a series of 2-hydroxy-3(trimethylammonium)propyl starches (HTPS) with different molar masses and cationic degrees that are potentially useful for EOR. It was investigated surface/interfacial tensions, rheological profile, emulsion index and wettability alteration. The results provide experimental evidence that the HTPS intrinsic properties affect the measured properties. The HTPS solution/oil interfacial tension (IFT) ranged from a low value of 19.0 to a high value of 34.0 mN/m and correlates positively with the molar mass of the HTPS. In contrast, the rheological behavior displays correlations with the molar mass and the degree of cationization. Furthermore, the 1 % HTPS solutions presented around 10 % of viscosity increase in comparison to brines typically used in waterflooding. The derivative with a higher molar mass and intermediate degree of cationization (HTPS 2) was more effective in changing the wetting condition of an aged limestone with a wettability alteration index (WAI) of 52 % while the commercial surfactant cetyltrimethylammonium bromide (CTAB) presented a WAI of 32.6 %.