SPI-slope/PIT-slope mapping as a guiding tool for the selection of technical grade surfactants for chemical enhanced oil recovery

Abstract

Hydrophilicity is a key property of surfactants, but it is difficult to quantify in absolute terms since it depends both on their molecular structure and on external parameters, especially salinity and temperature. When it comes to complex mixtures of technical grade surfactants, as the ones used in industrial applications, it is even more complicated. The PIT-slope and the SPI-slope are surfactants characterization methods based on the perturbation of a well-defined reference system by the surfactant under study. They allow quantifying the hydrophilic/lipophilic ratio and the sensitivity of surfactants as regards to temperature (PIT-slope) and salinity (SPI-slope). The study herein applies these methods to characterize technical grade surfactants used in chemical Enhanced Oil Recovery (EOR), which belong to the classes of polyethoxylated alcohols, alkyl benzene sulfonates and alkoxylated sulfates and carboxylates. The surfactants are positioned in a SPI-slope/PIT-slope map and we hypothesize that two surfactants, alone or in mixture, with the same position in this map show analogous interfacial behaviors. We illustrate how to use this tool to identify several surfactant mixtures providing the “optimal formulation” at the same salinity, for a given crude oil at the reservoir temperature. From a known binary surfactant mixture that forms a three-phase system (Winsor III) with a given crude oil, two other systems with the same position in the SPI-slope/PIT-slope map are formulated and evaluated.