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Abstract
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Nanofluid injection is a technique used for enhanced oil recovery (EOR). The performance of nanofluids varies in the presence of different salts. Na+, Mg2+, and Ca2+ cations are among the most common ions found in the formation water, which affect oil recovery through different mechanisms. Mg2+ and Ca2+ ions can change water and oil systems, because of their proper load density. The polar components of oil migrate toward water/oil interface in the presence of some ions. As a result, interfacial tension decreases and, consequently, the stability of water-in-oil (w/o) emulsion increases. Smart water (i.e., ionically modified water) injection in carbonate reservoirs has been developed during the past decade. In this study, smart water as well as a nanofluid were injected into an oil reservoir containing various types of cations with different salinities. The effects of different salts on the performance of Fe3O4/chitosan nanocomposite (synthesized in the previous studies for EOR) for emulsion stability were studied for the first time. The mean droplet area (MDA) of water in oil formed at 4000 psi, was measured in different scenarios. According to the findings, Mg2+ cation, compared to other cations results in a more stable emulsion. Na+ cation, at different concentrations, reduces emulsion stability by breaking the bond formed between Mg2+ and polar components of oil. The presence of Ca2+ at the low concentration increases the emulsion stability. Based on the findings of the present study, the synthesized nanocomposite increases emulsion stability. Low concentration of divalent cation increases stability while high concentration of this cation reduces emulsion stability in the presence of nanocomposites. The monovalent cation, at any concentration, reduces the performance of the nanocomposites for emulsion stability.
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