Effects of the water-oil volume ratio and premixing or pre-equilibration on the interfacial tension and phase behavior of biphasic mixtures

Relationship of Various Interfacial Tensions of Surfactants/Brine/Oil Formulations to Oil Recovery Efficiency

“…Phase behavior tests were done by mixing 12 mL of an aqueous surfactant solution in the synthetic brine (ρ = 1.004 g·mL –1 ) with 12 mL of crude oil (ρ = 0.887 g·mL –1 ) by vigorously shaking by hand. This method was shown to lead oil/water mixtures much closer to equilibrium than two other methods . For this reason, the same method was used when rock particles were also present.…”

“…The mixture was centrifuged for 1.5 h at 12,000 rpm (at an average acceleration of 19,800 g) to accelerate the phase separation process and the particle or droplet sedimentation, creaming, and coalescence. More details of the cleaning procedures and the phase behavior protocols were described in our previous work . Berea Sandstone particulate samples were prepared by grinding 10 g of the sandstone material for 1 min with a ceramic mortar and pestle.…”

“…The absolute and relative concentrations of the various surfactant components in the aqueous phase change upon flow in a porous reservoir and contact with the oil and the rock, because of (a) the overall and preferential partitioning of surfactants between the oil and aqueous phases and (b) surfactant losses due to adsorption on reservoir rock surfaces. − If a middle-phase microemulsion forms during an oil recovery process, then the number of relevant IFTs at each location increases from one, the IFT between the oil and the aqueous phase, to three, one between the oil phase and the aqueous phase, a second one between the oil phase and the microemulsion phase, and a third one between the aqueous phase and the microemulsion phase. The partitioning of surfactant and crude oil components is expected regardless of the brine salinity.…”

“…Then, the EIFT up,rock is determined between the pre-equilibrated surfactant brine solution and an oil drop. The EIFT p , type III, is defined as the equilibrium IFT between an oil and an aqueous phase after they have pre-equilibrated in the absence of rock . The EIFT p,rock , type IV, is the EIFT between an oil and an aqueous phase after they have pre-equilibrated with rock.…”

“…Finally, an EIFT eff , type V, is defined as that between an oil and an aqueous layer produced after a laboratory-scale core flood experiment. The EIFTs of types III, IV, and V depend on the volume ratio of the aqueous and oil phases, because the amounts of the partitioned surfactant components depend on the volume of each phase . Because IFTs are not measured directly during recovery processes, the EIFTs of type IV and type V are probably the ones are the most similar to them.…”