Alkaline flood is a cost-effective enhanced oil recovery (EOR) process, particularly suitable for acidic oil reservoirs. After alkaline solution is injected into an oil reservoir, some surfactants can be generated in situ by the neutralization of the injected alkali with the organic acids in crude oil. Such generated surfactants can be absorbed at the oil-water interface and dissolved in the bulk aqueous phase and/or in the oil phase as well, depending on their affinities for the aqueous and oil phases. The distributed surfactants change the interfacial tension (IFT) between the oil and aqueous phases. Therefore, a thorough study of this dynamic IFT phenomenon improves one's understanding of alkaline flood process. In this paper, the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case is employed to measure the dynamic IFTs between crude oil and different aqueous solutions. It has been found that the measured IFT changes with time and this dynamic IFT phenomenon is interpreted in terms of the surfactant generation and distribution at the oil-water interface, as well as the diffusion processes in the bulk phases. Meanwhile, it has also been observed that the volume of the pendant oil drop in an alkaline solution decreases with time. The so-called oil shrinking effect has been quantified and three possible mechanisms for this effect are proposed. These mechanisms include oil volatility in an aqueous solution, chemical reactions between the oil phase and the alkaline solution, and possible migration of water micro-droplets from inside the oil drop to the alkaline solution. More specifically, the dynamic IFT phenomenon and the oil shrinking effect are examined for a series of aqueous systems, such as deionized ultrafiltered water, and the alkaline solutions with different alkali concentrations. This study not only provides an improved understanding of the interactions between the oil and alkali but also helps to fully develop the oil recovery potential of an alkaline flood process.
It has long been recognized that alkaline flood is a cost-effective enhanced oil recovery (EOR) process, particularly suitable for acidic oil reservoirs. When the acidic crude oil and alkali are encountered in the alkaline flood, one of the most important phenomena in this process is the interfacial tension (IFT) reduction due to the in situ generation of surfactants by the chemical reaction of the organic acids in the crude oil and the alkali in the flood water. Such generated surfactants can be absorbed at the oil-water interface and gradually dissolved in the bulk aqueous phase and/or in the oil phase, depending on their affinities for the aqueous and oil phases. Thus, IFT between the oil phase and alkaline solution changes during an alkaline flood and finally reaches an equilibrium value.
In the literature, some efforts were made to study this kind of dynamic IFT phenomenon. An experimental study was carried out by Reisburg and Doscher [1], who examined the effects of interface aging and sodium hydroxide concentration on IFT.
