Abstract
A large proportion of extant crude oil is found in carbonate reservoirs worldwide. Alkylbenzene sulfonates are inexpensive anionic surfactants but they cannot be used in these reservoirs due to their incompatibility with divalent ions and high adsorption on the rocks. This paper proposes the solution to that problem by blending this kind of surfactant with surface-active ionic liquids. Namely, a formulation containing sodium dodecylbenzene-sulfonate (SDBS) and cocosalkylpentaethoximethylammonium methylsulfate ([C1EG][MeSO4]) was designed for the application. Two optimal blends, at 40/60 and 73.7/26.3 SDBS/[C1EG][MeSO4] ratios, were found in synthetic seawater via equilibria and interfacial tension (IFT) studies. Core-fooding tests were carried out to check the performance of both blends. The frst blend ratio (40 wt% SDBS) was selected to defne an optimal formulation (1 wt% blend in synthetic seawater at 298.15 K) due to its better injectability, higher reduction of the IFT, lower adsorption, and better oil recovery. Attained tertiary oil recovery (18% of the original oil in place), with low blend adsorption (0.37 mgblend/grock), shows the promising performance of the solution. The main mechanism associated with improved oil recovery is IFT reduction. This work offers a signifcant advance in the application of natural petroleum sulfonates in carbonate reservoirs.
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