Microwave Spectroscopic Analysis Of Surfactant/Polymer Flooding: Interrelationships Between Chemical Slug Properties, Coalescence Phenomena, And Tertiary Oil Recovery
Authors: Wasan D.T. , Perl Jeffery P. , Milos Frank S. 
Published: December 2007

Abstract
Microwave Absorption Spectroscopy was employed to monitor the dynamic insitu oil saturation profiles during laboratory tertiary oil recovery profiles during laboratory tertiary oil recovery experiments in consolidated Berea cores. Experiments were performed using Salem crude oil and two different low concentration petroleum sulfonate systems.
Microwave analysis revealed distinctly different oil banking characteristics for the different surfactant systems. Low viscosity slugs were seen to channel, causing the formation of two oil banks, one upon surfactant injection and another upon polymer injection. The fractional oil flow showed two peaks with a decrease between production of the two oil banks. In contrast, in production of the two oil banks. In contrast, in tests with slugs exhibiting good mobility control the core exit oil saturation rose and remained above waterflood residual saturation coincident with the production of a single continuous oil bank.
Surfactant slugs exhibiting rapid coalescence produced oil in emulsion-free form, while slowly produced oil in emulsion-free form, while slowly coalescing systems produced primarily emulsified oil. Furthermore, tertiary oil recovery efficiency correlated almost directly with coalescence rates for the systems studied. Coalescence was found to be necessary for the prevention of oil reentrapment.
These observations combined with produced fluids analyses lead to a mechanistic description of oil banking and oil reentrapment processes.

Introduction
Various mechanisms have been suggested to explain the formation and propagation of crude oil banks in low concentration surfactant/polymer flooding. Hill discussed the development of models for oil displacement from porous media which prescribed ultralow interfacial tension as the key prescribed ultralow interfacial tension as the key parameter governing oil recovery efficiency. parameter governing oil recovery efficiency. Mobility control was recognized as a necessary factor in preventing the dispersion and bypassing of released oil. Foster provided a rule of thumb recommending surfactant slug/oil bank bulk viscosity ratios on the order of four to one. Recently, Chang presented a review of polymer flooding technology as well as his method for the determination of oil/water bank mobility in micellar-polymer flooding. Claridge described a method for the design of graded viscosity banks which provides control of viscous fingering possibly resulting in improved oil recovery.
Ultralow tension and controlled mobility together provided a possible mechanism of oil release and production from porous media. This mechanism did not, however, address itself to the optimization of oil recovery or the problem of handling produced emulsions which have been observed in produced emulsions which have been observed in both field and laboratory tests. Hill et al described the problem of adverse mobility ratios caused possibly by insitu formation of viscous emulsions. He recommended the addition of emulsion modifiers which would reduce bypassing and reentrapment by promoting coalescence, thereby providing a means of optimizing oil recovery. providing a means of optimizing oil recovery. Childress and Schecter and Wade concluded from a series of displacement experiments using pure hydrocarbons in model porous media that systems forming the least stable emulsions, as evidenced by rapid coalescence, resulted in the highest displacement efficiencies.
In a series of three papers Wasan, et al described experiments on the coalescence behavior of crude oil/low concentration aqueous surfactant systems in conjunction with laboratory TOR experiments. It was observed that coalescence rate correlated well with interfacial shear viscosity, but not with interfacial tension. A series of core flooding experiments suggested a direct correlation between oil recovery efficiency and coalescence rate. Hence they proposed that a coalescence mechanism was involved in the formation and propagation of oil banks.