Abstract
As most of the light and easy oil fields have been produced or are nearing their end-life, the emulsion stability is enhanced and water cut is increasing in produced fluid which have brought challenges to oil–water separation in onshore and offshore production trains. The conventional solution to these challenges includes a combination of higher chemical dosages, larger vessels and more separation stages, which often demands increased energy consumption, higher operating costs and larger space for the production facility. It is not always feasible to address the issues by conventional means, especially for the separation process on offshore platforms. Electrostatic coalescence is an effective method to achieve demulsification and accelerate the oil–water separation process. In this paper, a novel compact electrostatic coalescer with helical electrodes was developed and its performance on treatment of water-in-oil emulsions was investigated by experiments. Focused beam reflectance measurement (FBRM) was used to make real-time online measurements of water droplet sizes in the emulsion. The average water droplet diameters and number of droplets within a certain size range are set as indicators for evaluating the effect of coalescence. We investigated the effect of electric field strength, frequency, water content and fluid velocity on the performance of coalescence. The experimental results showed that increasing the electric field strength could obviously contribute to the growth of small water droplets and coalescence. The extreme value of electric field strength achieved in the high-frequency electric field was much higher than that in the power-frequency (50 Hz) electric field, which can better promote the growth of water droplets. The initial average diameters of water droplets increase with higher water content. The rate of increment in the electric field was also increased. Its performance was compared with that of the plate electrodes to further verify the advantages of enhancing electrostatic coalescence and demulsification with helical electrodes. The research results can provide guidance for the optimization and performance improvement of a compact electrocoalescer.
Highlights
The results showed that the collision frequency is mainly controlled by the turbulence and turbulent electrocoalescence works well for all simulated water contents
The results indicate that numerical results obtained by computational fluid dynamic coupling with a population balance model (PBM) are in good accordance with experiments
It can be concluded that once the high voltage power is on, water droplets with diameters less than 10 μm are rapidly coalesced under the electrical field
Summary
As the oil well’s production life increases, the water content in the oil grows. It is usually in the form of water-in-oil (W/O) emulsion or oil-in-water (O/W) emulsion, which depends on the value of water cut. The process of removing water at the platform is usually achieved in large horizontal separators with the help of gravity and demulsifying chemicals. It is time-consuming and expensive to make the water content below 0.5% during the treatment when the water cut reaches more than 90%. Compared with the other widely used or tried solutions, electrostatic demulsification is becoming more and more popular, both from environmental and economical points of view [12]
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