Phase Partitioning of Anionic and Nonionic Surfactant Mixtures
- Christos Koukounis (U. of Texas) | W.H. Wade (U. of Texas) | Robert S. Schechter (U. of Texas)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- April 1983
- Document Type
- Journal Paper
- 301 - 310
- 1983. Society of Petroleum Engineers
- 5.2.1 Phase Behavior and PVT Measurements, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.3.4 Scale, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.4.1 Waterflooding, 4.1.5 Processing Equipment, 5.7.2 Recovery Factors
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The efficiency of oil recovery by waterflooding can be greatly unproved by the addition of judiciously selected surfactants. Under certain conditions, when surfactant solutions are mixed with oil, microemulsions are formed that may be in equilibrium with an excess oil (Type 1). an excess aqueous phase (Type II), or both (Type III). The partitioning of the surfactant between those coexisting equilibrium phases is important to consider in the design of microemulsion processes for oil recovery. This is particularly true because different phases generally move at differing velocities within the pore spaces of an oil reservoir and therefore fractionation will occur in successive stages along the flow path. This leads to chromatographic separation of the surfactant molecules. The problem is complicated because all surfactant systems are blends of molecules, and chromatographic separation will result in a change in the optimal salinity of the surfactant system. Thus, a system that is initially optimized will not remain optimized during the course of the flood.
To examine the question of selective surfactant partitioning, we varied the composition of oil/water/ surfactant equilibrated systems so that they would pass through the optimal formulation region. The partitioning of anionic surfactants into the oil in Type I and Type III phase systems was small. Furthermore, binary and ternary mixtures of these surfactants were found to copartition; that is, little if any fractionation was detectable. Their collective behavior was intermediate between those of the pure components. Nonionic surfactants, unlike anionics, partition substantially into the oil phase in Type I and Type III phase systems. This was found to be an intrinsic properly of the surfactant structure and not unique to those nonionic surfactant systems that are polydisperse.
Selective fractionation also was found for polydisperse nonionic surfactants.
The appropriate surfactant and cosurfactant system for a micellar/polymer flood to obtain enhanced oil recovery requires careful optimization. The surfactant must be selected so that, under reservoir conditions, the interfacial tension (IFT) between oil and brine is dramatically reduced. Numerous studies have demonstrated that the surfactant/cosurfactant system that produces the required interfacial activity must have solution properties properly balanced between those in the aqueous and oleic phases. This balance is sensitive to the equivalent weight as well as the structure of the surfactant, the concentration and type of alcohol cosurfactant used, the ionic nature of the brine, and the composition of the oil.
Clearly, any mechanism that tends to change one of these factors will also tend to alter the oil recovery efficiency of a given formulation. Thus, it is imperative either to control or to allow for these disrupting mechanisms.
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