Revisiting the Phase Inversion Temperature as a Practical Tool for EOR Applications

Since the two oil crisis in 1973 and 1979, and nowadays with the petroleum resource depletion, Enhanced Oil Recovery techniques (EOR) have become one of the most promising fields of interest for oil producers. EOR techniques are based on injection of suitable aqueous surfactant mixtures to extract the residual oil trapped inside the well by capillarity forces. An ultra-low interfacial tension between the aqueous phase injected and crude oil is needed to extract petroleum oils thanks to a three-phase microemulsion. The obtention of this “optimal” formulation depends on the nature of surfactants added and on the salinity of this aqueous phase, but also on other parameters related to the well itself, the crude oil composition and the well temperature. “Optimal” formulations can be accurately predicted for pure oils from the semi-empirical HLD equation but the prediction are much less reliable for crude oils [1]. Traditionally, people carry out lengthy salinity scans with equilibrated formulations at the well temperature to identify the best surfactant system for a given crude oil. Our work highlights a new method to determine these EOR key parameters by detecting the “dynamic” Phase Inversion Temperature (PIT) of surfactant/crude oil/water systems. The PIT concept was introduced first for nonionic surfactants [2], but it is also relevant for the characterization of more complex systems containing crude oil and anionic/nonionic surfactants. Considering the PIT shifts as well as the shape of conductivity-temperature profiles obtained with crude oil, it is possible to infer useful information on the crude oil such as precise EACN, Winsor III relation between optimal salinity and temperature, and concurrently an estimation of the microemulsion solubilisation ratio [3]. This PIT study allows also to classify EOR surfactants regarding their hydrophilic behavior using the PIT-slope method [4] and to predict the hydrophilic range of their mixtures in case of EOR applications. By the quick evaluation of the surfactant system and the crude oil parameters, the study of the PIT in petroleum systems proves to be a real asset to help in EOR formulations. [1] SALAGER, J.L. et al, Techniques de l’Ingenieur, 2001, vol. 157, p. 2001. [2] SHINODA, K. et al, The Journal of Physical Chemistry, 1964, vol. 68, no 12, p. 3485-3490. [3] GHOSH, S. et al, SPE Journal, 2016, vol. 21, no 04, p. 1,106-1,125. [4] ONTIVEROS, J. F. et al, Journal of colloid and interface science, 2015, vol. 448, p. 222-230.