(465d) Effluent Analyses and Interfacial Tension Measurements for Laboratory-Scale Coreflood Oil Recovery Experiments

The effluents of laboratory-scale coreflood experiments are used for assisting the design of surfactant/polymer/brine formulations for chemical Enhanced Oil Recovery (cEOR) processes. The compositions of the effluents are expected to differ from those of the injected fluids due to the partitioning of water, and various surfactant, salt, and oil components among the oil phase, the aqueous phase, and the surface of the pores of the rock. Such chemical composition shifts cannot be estimated in the absence of multiphase flow and direct contact among the chemical formulations, the oil, and the porous core material. Thus, coreflood experiments are critical for evaluating formulations prior to field uses. The volumes, viscosities, and densities of the produced oil and aqueous phase, and the concentration of various components are determined as done generally in the literature. In addition, the interfacial tensions (IFTs) between several samples of the produced oil and several samples of the produced aqueous phase are determined. Based on results of several experiments to be presented here, our hypothesis is that the recovery efficiency of an injected aqueous surfactant solution can be maximized when the oil bank that may form in the early stages of the coreflood experiment mobilizes further the oil in the back portion of the core. The IFT values shift to higher values in our data as more oil interacts and equilibrates with the aqueous phase due to the losses of surface-active components. Then, less oil may be mobilized from the back portion of the core. This hypothesis is tested by measuring the oil recovery efficiency and the EIFT values from effluent samples. For our data with the higher oil recovery efficiencies, the EIFT values for the oil produced later were significantly lower than those with the oil produced earlier. For our coreflood data with lower oil recovery efficiencies, the EIFT values were similar. The oil banks for more successful coreflood experiments apparently formed during the early stages of the experiments, and then they mobilized the residual oil. These inferences are supported by the data of significant overall surfactant partitioning in the oil and by the preferential partitioning of the more surface-active components; see Chung, J.; Boudouris, B.W.; Franses, E.I. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2019, 571, 55-63. Therefore, we recommend determining several EIFTs for the coreflood experiment effluents to better screen and identify promising formulations.