Fast and accurate selection of surfactants for enhanced oil recovery by dynamic Salinity-Phase-Inversion (SPI)

Abstract

In conventional chemical Enhanced Oil Recovery (EOR), surfactant mixtures must be optimized to obtain the so-called “optimum formulation” characterized by a three-phase behaviour (WIII) and an ultra-low interfacial tension between crude oil and injected water. To attain this condition, discontinuous salinity scans of Surfactant-Oil-Water (SOW) systems are usually performed in a series of sealed pipettes maintained at the reservoir temperature until complete phase separation. Furthermore, some SOW mixtures do not give a WIII, but instead they form viscous phases which are very detrimental for EOR applications.The study herein describes a novel method called dynamic Salinity-Phase-Inversion (SPI) to quickly and accurately determine the optimum formulation and to anticipate whether the surfactant mixture will provide, by the conventional static method, a WIII or a viscous phase. This method consists in continuously modifying the salinity of a stirred SOW system at WOR in the vicinity of 1, in order to detect the phase inversion of the emulsion by a sudden drop in conductivity.The effectiveness of the method is illustrated by seeking the optimum formulation for two crude oils in the presence of a mixture of an ionic EOR surfactant (sulfated propoxylated n-alcohol) and a nonionic co-surfactant (ethoxylated i-alcohol), with or without alkali. Continuous salinity scan of the stirred SOW system maintained at constant temperature allows the identification of the optimal salinity within 30 min. This method therefore significantly accelerates the optimization of surfactant blends suitable for a given oil reservoir.