The Rules for Achieving High Solubilization of Brine and Oil by Amphiphilic Molecules

Abstract

Abstract The oil-recovery effectiveness of a chemical flood has been proved related to the phase behavior of the brine/oil/surfactant system. In particular, it is advantageous to formulate the system so that optimal threephase behavior is obtained. However, it also has been demonstrated that all the optimized systems are not equivalent in terms of solubilization. interfacial tensions (IFT's), and oil-recovery efficiency. This paper addresses the conditions that promote high solubilization in microemulsions, a property correlated to the values of the IFT and therefore correlated to the ability of such systems to displace the oil in porous media. When one formulation parameter is changed, another parameter must be varied at the same time for compensation to reoptimize the system. The mechanism of solubilization is investigated experimentally by considering the usual formulation parameters: salinity, oil type, alcohol type and concentration, and surfactant structure and type (anionics and nonionics). The results are interpreted in terms of interaction energies between surfactant, oil, and water. In particular, the role of the alcohol and its impact on the solubilization by amphiphilic systems are discussed in detail and interpreted. Moreover, the concepts developed in this paper explain the effect of the surfactant structure and therefore aid in the design of amphiphilic molecules exhibiting a high solubilizing power for given conditions of brine, temperature, etc. Introduction Mobilization and transport of residual oil by chemical-flooding processes involve various mechanisms that must be considered when formulating a surfactant slug, but, among them, it is well known that IFT's between phases play a major role. Reed and Healy have shown phases play a major role. Reed and Healy have shown that ultralow IFT's can be attained when a microemulsion phase (surfactant-rich phase, the so-called "middle phase (surfactant-rich phase, the so-called "middle phase") is in equilibrium simultaneously with an oil phase") is in equilibrium simultaneously with an oil phase and a water phase. They first have defined the phase and a water phase. They first have defined the concept of optimal salinity as being the point where the IFT's at the oil-middle phase and middle phase/water interfaces are equal. At that point, the volumes of oil and water solubilized in the middle phase generally are identical, although there is no theoretical basis for that. A correlation between the values of the quantities of oil and water solubilized in the middle phase and the values of the IFT's between the phases also has been found: the lower the tension, the higher the solubilization. Therefore, it appears judicious to start the screening procedure of surfactant systems for enhanced oil procedure of surfactant systems for enhanced oil recovery (EOR) by looking for the point where equal volumes of oil and water are solubilized in the surfactant phase of a three-phase system. During recent years, phase of a three-phase system. During recent years, much time has been devoted to discovering that point, and the rules for compensating changes in the formulation variables have been established for anionic and non-ionic surfactants. We must emphasize that, if we start from an optimized system and we change a formulation variable defining the system, the optimal state is lost, and another formulation variable must be changed to reach a new optimal state. All optimized systems are not equivalent, as shown in previous results, and consideration of the amount of previous results, and consideration of the amount of oil and water solubilized in such systems provides a criterion to compare them. In a previous paper, we carried out a systematic study of the effect of the formulation variables on the solubilization at optimum by anionic surfactants. Some results concerning nonionics have been presented recently presented recently. SPEJ p. 327