(308d) Various Interfacial Tensions of Pre-Equilibrated Surfactants/Brine/Oil Mixtures and Their Applications to Enhanced Oil Recovery Efficiency

The interfacial tension (IFT) reduction between trapped oil drops and the surrounding aqueous phases is critical for mobilizing oil droplets and improving enhanced oil recovery (EOR) efficiency. The addition of surfactants is the primary means to reduce IFTs. However, it is difficult to evaluate surfactant formulation candidates prior to expensive core flood tests in a robust way because the mixtures of surfactants, crude oil, and brine contain numerous components and conventional tensiometry and other characterization methods become challenging. In addition, the in-situ measurements of IFT values and their evolution throughout the recovery process are currently not possible, even during the laboratory-scale core flood tests. Therefore, it is critical to: (a) develop robust IFT measurement protocols that provide reliable IFT values and (b) extract reliable data from core flood tests in order to develop correlations between the surfactant formulation and their EOR performance. A robust protocol for determining reliable IFT values between aqueous commercial surfactant solutions and crude oil samples was demonstrated in our previous work (see: Chung, J.; Boudouris, B.W.; Franses, E.I. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2018, 537, 163-172). In this effort, we identify and compare five equilibrium IFT (EIFT) values from surfactant/brine/oil mixtures, including EIFTs from the effluent samples of core flood tests, EIFT_eff in order to develop a correlation between those EIFTs with the EOR efficiency from laboratory-scale core flood tests. The five EIFTs are the: (i) un-pre-equilibrated EIFT, EIFT_up, (ii) un-pre-equilibrated equilibrium IFT in the presence of rock (EIFT_up,rock), (iii) pre-equilibrated equilibrium IFT (EIFT_p), (iv) pre-equilibrated equilibrium IFT in the presence of rock (EIFT_p,rock), and (v) effluent equilibrium IFT (EIFT_eff). By comparing such EIFTs we anticipate observing the effects on the phase behavior and IFT from oil and water transfer across the oil/water interfaces, surfactant component partitioning to the oil phase, and surfactant adsorption on rock surfaces. Based on results of several new core flood experiments, our hypothesis is that most or all of the EIFT values between the progressing surfactant solutions and trapped oil droplets should remain low to ensure high recovery efficiency. To test the hypothesis, we compared the EIFT_up and EIFT_up,rock that are related to the initial stages of the recovery process to the EIFT_p, EIFT_p,rock and EIFT_eff that are related to the later stages of the recovery process. For our data with the higher oil recovery efficiencies, the EIFT_up, EIFT_up,rock, EIFT_p, and EIFT_p,rock values were ultralow, less than 0.01 mN m^-1, or low, less than 0.1 mN m^-1. In addition, the EIFT_eff with the oil that was produced in the later stages were significantly lower than those with the oil produced in the earlier stages. Therefore, we recommend comparing five EIFTs, including one from the core flood effluents, for robust evaluation of surfactant formulations prior to the pilot tests for better screening and identifying promising formulations.