Deactivation of Petroleum Sulfonates by Crude Oil
Authors: Clementz David M. , Gerbacia W.E. 
Published: December 2007

Introduction

Tertiary oil recovery processes that use petroleum sulfonates to mobilize residual oil require that the injected chemicals be propagated through the reservoir to provide a continual source of surfactants at the oil/water interface. Yet, experimental and field evidence has suggested that surfactants are depleted continually from the injected fluid bank by two primary mechanisms: adsorption on rock surfaces and precipitation as insoluble salts because of contact with reservoir brines.

Recent experiments have suggested that another surfactant depletion mechanism exists that can be significant. Petroleum sulfonates can lose their interfacial activity through infiltration of the active sulfonate "head" by molecular components of the crude oil. While the nature of the deactivation mechanism is not fully understood, the results allow discussion of possible effects that this deactivation may have on surfactant flooding.

Sulfonate Determination Method

Discovery of this deactivation was made possible through use of a new method of sulfonate analysis. Until recently, the available methods of sulfonate detection have been ineffective in dark-colored crude oils and brines (the colorimetric hyamine and methylene blue techniques) or time consuming (liquid chromatography). A new method, the radiometric sulfonate determination, has been developed and applied to this problem. Rapid and accurate, the method is not limited by the color of the parent phase. Thus, direct detection of "free" sulfonates parent phase. Thus, direct detection of "free" sulfonates in crude oil samples is possible.

Detection of sulfonates in groundwater and potable water using this new method has been demonstrated clearly by Taylor and Waters. Their method has been modified slightly to best accommodate oil samples. The basis for this analysis is the reaction between sulfonates and a very stable chloroform-insoluble complex cation, ferroin [Fe(II) (1, 10-phenanthroline), which is radioactively labeled Fe-59. A chloroform-soluble product is formed through the following equation: product is formed through the following equation:

The amount of radioactively labeled ferroin extracted into the chloroform is therefore directly proportional to the amount of sulfonate present. A small sample of sulfonate-containing liquid (either oil or water) is introduced into an aqueous ferroin/chloroform mixture and is extracted. The chloroform layer is counted and the concentration is determined from a standard curve.

Discussion of Results

Petroleum Sulfonate 425 (P.S. 425), a sulfonated Petroleum Sulfonate 425 (P.S. 425), a sulfonated distillate fraction of a California crude oil prepared by Chevron Chemical Co., was used in this study as a model system because it is completely soluble in oil. Solutions of P.S. 425 in Chevron Base Oil C (a colorless kerosene) were analyzed by both the radiometric method and the traditional hyamine titration, and the results were in excellent agreement.

Introduction of the sulfonate into crude oil yielded an unexpected result. Ten 5-ml samples of P.S. 425 in Base Oil C, all at different initial concentrations, were mixed with 5-gm samples of crude oil. Fig. 1 shows the concentration actually measured in the resulting solutions compared with the ideal curve of P.S. 425 in an equal amount of Base Oil C. Clearly, the amount measured in the crude oil is significantly lower than that in the base oil, and the incremental amount (slope) measured is also less. Beyond 225 microequivalents (mueq) per 5 gm (verified experimentally to 2,000 mueq per 5 gm added), the line parallels the ideal line. Independent verification of this parallels the ideal line. Independent verification of this result has been obtained using a tedious modified methylene blue technique.

JPT

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