Electromagnetic separation provides a new way to treat oilfield produced water. In this paper, the process of electromagnetic separation of oilfield produced water is analyzed theoretically and numerically, and the separation characteristics are investigated when TOC is 103 ppm and the viscosity and size of oil droplets are 100 Pa.s and 101 μm, respectively. The results show that: 1) the electromagnetic separation of oilfield produced water has advantages of supergravity separation and air flotation separation, and the separation efficiency is high; 2) with the same supergravity coefficient, the treatment capacity of produced water increases with the size of oil droplets increasing, and decreases with TOC and the viscosity of oil droplets increasing; 3) the flow rate of discharged water increases with the increase of the supergravity coefficient and oil content of discharged water; 4) the flow rate of produced water, that is, the treatment capacity of the separation channel increases with the increase of the supergravity coefficient.
Nowadays, the exploitation of most oilfields in China has been entered in the middle and late stage with a comprehensive water content more than 80% or even more than 90%. Water drive, thermal recovery, steam flooding, chemical flooding and other methods have been used, resulting in the complexity and variability of produced water. And in produced water, the water phase exists in the form of free water, and the oil is mixed into the water phase mainly in the form of dispersing small oil droplets of 20-150 μm. There is also a small content of emulsified oil of 5-20 μm in produced water (Almeida et al, 2019; Kundu et al, 2018). For the separation of free water, it can generally be achieved by gravity sedimentation and centrifugal separation (Yang et al, 2021). For the emulsions, the first thing to do is to demulsify and heating, chemical and electric de-extraction methods are usually used. The membrane separation, air flotation, flocculation, adsorption and filtration have been used in the deep treatment of oily sewage (Ahmadun et al, 2009; Chen et al., 2019; Yu et al 2013). At present, the treatment of produced water is more and more difficult. It is almost impossible for a single oil-water separation method to meet the increasing separation requirements, and multiple methods are combined to achieve cost-effective separation results (Su et al., 2019). And many new methods have been proposed and used to improve the effectiveness, efficiency and environmental friendliness. An environmentally friendly and recyclable biofilm with immobilized cells of P.aeruginosa NY3 was developed for the treatment of produced water with high salinity and low pH (Nie et al, 2020). Oil well produced water was treated by a biochemical double membrane process in Shenli Oilfield and the oil content of produced water after biochemical treatment was 0.63 mg/L (Pan et al, 2021). Lu and et al (2021) applied the thermochemical cleaning method first to treat the polymer-containing produced water and got an average oil recovery rate increased by 20%. A novel liquid-liquid extraction and efficient phase separation in a mixer-settler based on phase inversion was put forward, the oil and grease removal from real offshore produced water samples was evaluated and a final outlet stream containing oil and grease under 29 mg/L was got (Ana Caroline Klemz et al, 2021).
