Crude alkaline solution interface

This paper presents observations on the difference in behavior of emulsification processes which can occur during surfactant and caustic flooding in enhanced recovery of petroleum. Cinephotomicrographic observations on emulsion characteristics generated at the California crude oil-alkaline solution interface as well as in the Illinois crude oil-petroleum sulfonate system are reported. The interdroplet coalescence behavior of oil-water emulsion systems appear to be quite different in enhanced oil recovery processes employing various alkaline agents as opposed to surfactant/polymer systems. 

Alkaline flooding is an old concept, first patented by Atkinson (48) in 1927. Hydroxide ion in an alkaline solution reacts with acidic components present in some crude oils to produce petroleum soaps, which are generally sodium salts of carboxylic acids. These petroleum soaps are capable of adsorbing at the oil-water interface and lowering interfacial tension. Crude oils suitable... 

Emulsification mainly depends on the water/oil IFT. The lower the IFT, the easier the emulsification occurs. The stability of an emulsion mainly depends on the film of the water/oil interface. The acidic components in the crude oil could reduce IFT to make emulsification occur easily, whereas the asphaltene surfactants adsorb on the interface to make the film stronger so that the stability of emulsion is enhanced. The extracted oil cannot be easily emulsified with alkaline solution because of the high IFT. However, the externally added surfactants can reduce the IFT between the extracted oil and mixed solution to a low value so that the emulsification can occur. 

The interfacial tension between the crude oil and the alkaline solution is a strong function of the age of the interface. The interfacial tension increases with the age of the interface. 

There exist natural surface-active substances in crude oil, such as petroleum acids and asphaltenes. The ionized acids formed by the reaction between the petroleum acids and the alkali can decrease the interfacial tension [1,5-7] and accelerate the thinning and breakdown of the film. At the same time, the asphaltenes can adsorb on to the interface and improve the stability of the film. When the film thickness is small enough (< 100 nm), it can keep this value for a long time because of the stabilization of the asphaltenes in the oil. In our study, almost all crude oil/alkali systems have this drainage process, and the crude oil/brine systems do not show it. So we can conclude that the drainage is correlated with the components, which have the interactions with alkaline solutions. 

The point at which, supposedly, 50% of the acid species is transformed in salt corresponds to the half-neutrahzation, i.e., when half the alkahne required to reach the equivalence point has been added. This position corresponds to a buffer zone in which the variation of pH is small with respect to the amoimt of added neutralization solution (Fig. 14 left plot). Hence, in this region a very slight variation of pH can produce a very large variation of neutralization (Fig. 14 right plot), i.e., a considerable alteration of the relative proportion of AH and A . Far away from this pH, the opposite occurs. Consequently, the pH could be used to carry out a formulation scan, but the scale is far from hnear and the variation of pH does not render the variation of the characteristic parameter of the actual surfactant mixture that is at interface [77,78]. The appropriate understanding of the behavior of this kind of acid-salt mixture is particularly important in enhanced oil recovery by alkaline flooding [79,80] and emulsification processes that make use of the acids contained in the crude oils [81-83]. 

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