(718c) Dynamic Measurement Method of the Emulsified Water Content Based on Interfacial Polarization

Dynamic Measurement Method of the Emulsified Water Content

Based on
Interfacial Polarization

Oil-water two-phase system in the flow shear conditions tends to
form a certain stable emulsion, affecting the flow characteristics of oil-water
two-phase in gathering lines. Compared to the quiescent state, the emulsion in
the flowing state has a higher emulsified water content. Conventional
emulsified water content studies are usually based on static conditions. The
objective of this study is to propose an effective method for measuring the
emulsified water content of oil-water two-phase system under flowing
conditions.

There are interfaces films between oil and water phase in crude
emulsions because of the existence of some natural surfactants including
asphaltenes, resins, and naphthenic acids et al. In the alternating electric
field, the charged particles will accumulate on interface film, which caused
the interfacial polarization. According to the difference between the
conductivity of oil phase and water phase, and the polarization of the phase
boundary film, the emulsion system in the alternating electric field can be
equivalent to a circuit model composed of resistors and capacitors in series or
in parallel. Based on the circuit model, the complex impedance formula capable
of describing of emulsion system is thus deduced. There exists a maximum value
of the response curve of imaginary part of complex impedance due to the
occurrence of interfacial polarization of emulsion. The corresponding frequency
of imaginary maximum is defined as the interfacial polarization frequency f₀(w), which is strongly
correlated to the water content of the emulsion.

A dynamic testing apparatus (Figure 1) of complex impedance of
emulsion is developed in our work based on the principles stated above. To
realize the dynamic testing and improve the sensitivity of the measurements,
the storage tank is made of non-metal material with two half-cylindrical
surface electrodes. The measuring circuit is based on a Frequency Response
Analyzer PSM1700, which is used to measure the impedance of emulsions in the
frequency range of 50Hz-1MHz.

Using this apparatus, different stirring rates and test
temperatures were controlled for the oil-water mixtures with different water
contents in experiments to prepare emulsions with varied amount of emulsified
water content. The experimental results suggest linear relation for the
interfacial polarization frequency and emulsified water content of the
oil-water emulsions in the observed range. The relationship between the
emulsified water content C_e
and the interfacial polarization frequency f₀(w) can be well described by C_e=k₁f₀(w)+k_2,
The coefficients k₁(<0)
and k₂ are obtained by linear fitting with the
temperature and the shear rate, respectively.

Furthermore, it is found that the value of interfacial frequency
will significant step increase when the phenomenon of full emulsification
occurs. In this way, the step increase in interfacial frequency can be used to
determine the complete emulsification of the oil-water mixture.

Fig. 1 Dynamic testing apparatus of
emulsion