Abstract
The combination of chemical enhanced oil recovery (CEOR) and low salinity water (LSW) flooding is one of the most attractive enhanced oil recovery (EOR) methods. While several studies on CEOR have been performed to date, there still exists a lack of mechanistic understanding on the synergism between surfactant, alkali and LSW. This synergism, in terms of fluid–fluid interactions, is experimentally investigated in this study, and mechanistic understanding is gained through fluid analysis techniques. Two surfactants, one cationic and one anionic, namely an alkyltrimethylammonium bromide (C19TAB) and sodium dodecylbenzenesulfonate (SDBS), were tested, together with NaOH used as the alkali, diluted formation brine used as the LSW, and the crude oil was collected from an Iranian carbonate oil reservoir. Fluids were analyzed using pendant drop method for interfacial tension (IFT) measurement, and Fourier transform infrared spectroscopy for determination of aqueous and oleic phase chemical interaction. The optimum concentration of LSW for IFT reduction was investigated to be 1000 ppm. Additionally, both surfactants reduced IFT significantly, from 28.86 mN/m to well below 0.80 mN/m, but in the presence of optimal alkali concentration the IFT dropped further to below 0.30 mN/m. IFT reduction by alkali was linked to the production of three different types of in situ anionic surfactants, while in the case of anionic and cationic surfactants, saponification reactions and the formation of the C19TAOH alcohol, respectively, were linked to IFT reduction. The critical micelle concentration and optimal alkali concentration when using cationic C19TAB were significantly lower than with the anionic surfactant; respectively: 335 vs 5000 ppm, and 500 vs 5000 ppm. However, it was found that SDBS was more compatible with NaOH than C19TAB, due to occurrence of alkali deposition with the latter beyond the optimal point.
Highlights
Increasing demand for crude oil and their limited resources have forced petroleum production companies to use enhanced oil recovery (EOR) methods
One of the most commonly adopted Chemically enhanced oil recovery (CEOR) processes is surfactant flooding, which has been shown to improve oil recovery significantly.[1−8] Oil recovery extent is a function of rock and fluid properties, such as pore structure, capillary pressure, interfacial tension (IFT), rock wettability, mobility ratio, and reservoir heterogeneity
Significant research has been carried out on the effects of alkali and surfactants to reduce the interfacial tension between oleic and aqueous phases, there has been a lack of mechanistic understanding to define the chemical reactions between the crude oil and chemical slug in detail
Summary
Increasing demand for crude oil and their limited resources have forced petroleum production companies to use enhanced oil recovery (EOR) methods. Enhanced oil recovery (CEOR) is one of the most effective EOR methods in beneficially altering reservoir rock and fluid properties, enabling increased crude oil production. Kumar et al.,[20] investigated the interfacial interaction of four different types of cationic surfactants, including C10TAB, C15TAB, C16TAB, and C19TAB, as well as their effects on wettability alteration of oil-wetting reservoirs. They reported critical micelle concentration (CMC) of C10TAB, C15TAB, C16TAB, and C19TAB to be 120, 14, 0.9, and 1 mM, respectively. The IFT between crude oil and C10TAB, C15TAB, C16TAB, and C19TAB, at their respective CMC concentrations, were found to be 7, 0.23, 7.6, and 0.5 mN/m, respectively.[20]
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