Browsing by Autor "Robert Schechter"

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Mixing Rules for Optimum Phase-Behavior Formulations of Surfactant/Oil/Water Systems
(Society of Petroleum Engineers, 1979) Jean‐Louis Salager; Maurice Bourrel; Robert Schechter; W. H. Wade
Abstract Many formulations used in surfactant flooding involve blends of surfactants designed to glue the best oil-recovery efficiency. Because oil-recovery efficiency usually is presumed to relate closely to surfactant/brine/oil phase behavior, it is of interest to understand the effect of mixing surfactants or of mixing oils on this phase behavior.We show that a correlation defining optimal behavior as a function of salinity, alcohol type and concentration, temperature, WOR (water/oil ratio), and oil type can be extended to mixtures of sulfonated surfactants and to those of sulfonates with sulfates and of sulfonates with alkanoates, provided the proper mixing rules are observed. provided the proper mixing rules are observed. The mixing rules apply to some mixtures of anionic and nonionic surfactants, but not to all. These mixtures exhibit some properties that may be of practical interest, such as increased salinity and practical interest, such as increased salinity and temperature tolerance. Introduction Recent studies have shown that formulation of the surfactant/brine/oil system is a key factor governing the performance of microemulsions designed to recover residual oil. These studies demonstrate that all optimal formulations exhibit characteristic properties that are remarkably similar. In general, properties that are remarkably similar. In general, the optimal microemulsion can solubilize large quantities of oil and connate water; in the presence of excess quantities of oil and water, a third surfactant-rich middle phase is formed. The interfacial tensions (IFT's) between the excess phases and the surfactant-rich phase are both low - about 10 dyne/cm (10 mN/m). Given an oil/brine system from a particular reservoir, one can achieve this formulation by varying the surfactant or the cosurfactant. Different oils, brines, or temperatures require formulations correspondingly altered to maintain optimal conditions. Previous studies have shown that the three-phase region exists over a range of values when one parameter, such as cosurfactant concentration, parameter, such as cosurfactant concentration, salinity, temperature, etc., is varied systematically (often called a scan). Thus, some ambiguity may exist with regard to the selection of those parameters representing the optimal formulation. Clearly, the optimum is that which recovers the most oil. However, tests are laborious, difficult to reproduce precisely, and sensitive to other factors, such as precisely, and sensitive to other factors, such as mobility, surfactant retention, wettability, etc. Therefore, it is desirable to impose an alternative definition that can be used for screening, though the final design still is dictated by core floods.Healy and Reeds have shown that the optimal formulation for oil recovery closely corresponds to that for which the IFT's between the excess oil and water phases and the surfactant-rich phase are equal. An almost equivalent criterion also was shown to be that point in the three-phase region for which the volume of oil solubilized into the middle phase equals the volume of brine. Furthermore, Salager et al. have used still another criterion that seems to be essentially equivalent to those used by Healy and Reed - an optimal salinity is defined as the midpoint of the salinity range for which the system exhibits three phases.These criteria are useful because they permit the screening of microemulsion systems using simple laboratory tests. SPEJ P. 271
Properties Of Amphiphile/Oil/Water Systems At An Optimum Formulation For Phase Behavior
(1978) Maurice Bourrel; Andrew M. Lipow; W. H. Wade; Robert Schechter; Jean‐Louis Salager
Abstract The oil recovery effectiveness of a chemical flood has been shown to be related to the phase behavior of the brine-oil-surfactant system. In particular, it is advantageous to formulate the system particular, it is advantageous to formulate the system so that middle phases are formed. There are, however, an infinite number of surfactant cosurfactant (alcohol) combinations which will give the desired phase behavior. The selection of the preferred system out of this infinity of possible systems is an optimization problem and is the subject of this paper. problem and is the subject of this paper. An extensive study of the interfacial tension of dodecyl ortho xylene sulfonate sodium salt, as a function of salinity, alcohol and hydrocarbon molecular weight has been conducted. The results reveal that certain formulations may be preferred since the interfacial tension of some systems at optimum conditions is smaller than others. Indeed, conditions giving a global interfacial tension minimum were found. It is also known that for enhanced oil recovery, it is desirable to maintain miscibility between the chemical slug and the reservoir fluids as long as possible. This means that the height of the possible. This means that the height of the multiphase region should be minimized. This study show that the height can be minimized by a proper formulation. Introduction A correlation relating the variables deft optimum systems for improved oil recovery has be reported. This equation gives the optimum salinity, S*, as a function of the alkane carbon number of the oil, ACN, the alcohol and a parameter, sigma, which is characteristic of the surfactant as follows: (1) where K is a constant equal to 0.16 for all alkylaryl sulfonates and f(A) is a function of alcohol type and concentration known for alcohols heavier than C5. The dots indicate that other variables, such as the water-oil ratio (WOR) and the temperature, have been omitted since they are not considered in this work. Equation 1 applies if WOR = 4 and T = 25 degrees C. The ratio sigma/K has been called the EPACNUS and is the extrapolated preferred alkane carbon number at unit salinity and preferred alkane carbon number at unit salinity and without alcohol, since f(A) is defined so that it vanishes as the alcohol concentration goes to zero. Equation 1 represents a plane in the space in S,ACN and f(A) as shown in Figure 1, and any point on this plane is an optimum system in the following sense. For a given oil and surfactant system, a middle phase will be observed over a range of salinities and the midpoint of this salinity range will be called the optimum salinity. Furthermore, the surfactant system is said to be an optimum one. This implies that a series of experiments in which a property important to improved oil recovery, such property important to improved oil recovery, such as interfacial tension or amount of surfactant needed to solubilize certain volumes of water and oil, will yield a minimum value of the property when a point on the plane is reached. Thus, a series of interfacial tension measurements will reveal a minimum value at the point where line 4 shown in Figure 1 pierces the plane. (Perhaps, it would be more pierces the plane. (Perhaps, it would be more precise to assert that the minimum will occur in the precise to assert that the minimum will occur in the vicinity of the plane rather than on it. This point is further clarified in a subsequent section.) If the experiment is repeated at a different salinity or alcohol concentration or both, then the minima of the properties in question will be found at the new point at which a vector parallel to line 4 intersects the plane. If the values of the minima are different at the two points, then one point on the plane may be preferred to the other with regard to plane may be preferred to the other with regard to efficiency of oil recovery. Thus, it is appropriate to ask if all points on the optimum plane are equivalent with regard to oil recovery. This is the question addressed in this paper.