Effect of hydrolyzed polyacrylamide used in polymer flooding on droplet–interface electro-coalescence: Variation of critical electric field strength of partial coalescence

Abstract

Polymer flooding is widely used in petroleum industry to enhance oil recovery. However, presence of polymer molecules in produced liquids can influence the droplet coalescence at oil-water interface in electric dehydration separators. In this study, the influence of hydrolyzed polyacrylamide (HPAM) on droplet-interface coalescence was examined through high-speed recording and observation. Deformation of droplets of aqueous polymer solution under electric fields was experimentally observed. The images showed droplets collapsed to filament without pinch-off due to viscoelasticity. Meanwhile, fine secondary droplets erupted from the summit of filament, which was detrimental to dehydration efficiency. A critical electric field strength (Ecrit) beyond which partial coalescence occurred was identified. The effects of the initial droplet size, HPAM concentration, electric field waveform and frequency were explored. The results showed that Ecrit increased with the decrease in initial droplet radius or the increase in HPAM concentration. Four kinds of AC or pulsatile electric fields (PEFs) were used including sinusoidal AC (sine AC), square, pulsed DC (PUDC) and pulsed AC (PUAC) waveforms. The increase in frequency suppressed the electro-induced stretching of droplets in the vertical direction, inhibiting partial coalescence. For these different electric fields, the increase in Ecrit with elevated frequencies followed different ways. Overall, Ecrit of square waveform was larger than those of other waveforms; however, Ecrit of PUAC and sine AC waveforms may exceed that of square waveform at high frequencies. These findings are useful for the development of electro-dehydration separators for oils containing dissolved polymers in the dispersed aqueous phase.

Unraveling Partial Coalescence Between Droplet and Oil–Water Interface in Water-in-Oil Emulsions under a Direct-Current Electric Field via Molecular Dynamics Simulation

“…In alkali-surfactant–polymer flooded crude oil, a high concentration of sodium carbonate (Na 2 CO 3 ) increased the conductivity of the water droplets, causing a decrease in the charge relaxation time and, consequently, an increase in the critical field strength ( E c ) . Adding hydrolyzed polyacrylamide (HPAM) to the aqueous phase increased the viscoelasticity of the droplet, thereby inhibiting the partial coalescence behavior . Owing to the decreasing oil–water IFT, sodium dodecyl sulfate would facilitate the formation of daughter droplets .…”

“…17 Adding hydrolyzed polyacrylamide (HPAM) to the aqueous phase increased the viscoelasticity of the droplet, thereby inhibiting the partial coalescence behavior. 18 Owing to the decreasing oil−water IFT, sodium dodecyl sulfate would facilitate the formation of daughter droplets. 19 Silica (SiO 2 ) nanoparticles could both increase the conductivity of the dispersion phase (water) and decrease the oil−water IFT, while the dominance of these effects on partial coalescence shifted with increasing field strength.…”

Response surface methodology for modeling of the critical electric field of a single drop subjected to different electric waveforms

“…By exceeding the critical field strength, devastating effects like Taylor cone will appear at drop's ends and on the water-oil interface and also drops decline to coalesce with one another or with water-oil interface [5,19,[23][24][25][26][27][28]. Achieving the critical electric field depends on a variety of variables such as type of applied waveform, frequency, drop diameter, interfacial tension and some other variables [29][30][31][32][33][34]. Disadvantages of utilizing a DC electric field, such as corrosion, great energy consumption and short circuit, make using pulsatile electric field (PEF) an inevitable selection in the electro-coalescence technology.…”

Deformation and breakup of water droplets containing polymer under a DC electric field

“…[8][9][10][11] Nevertheless, with the extensive application of polymer flooding technology, the emulsion contains a large number of polymer molecules, easily leading to a significant rise in the electric current and the collapse of electric field. 12,13 This will stop the electric dehydrator from working and deteriorate the oil-water separation efficiency, seriously restricting the development and application of electrostatic demulsification technology. Studying the dynamics of deformation and breakup of droplets containing polymer under the electric field is conducive to understanding the mechanism of electric field collapse, which provides valuable insights for resolving this difficulty.…”

“…Especially for petrochemical industry, the high voltage electric field is widely used to demulsify the water‐in‐oil emulsion in the oil field and refinery 8–11 . Nevertheless, with the extensive application of polymer flooding technology, the emulsion contains a large number of polymer molecules, easily leading to a significant rise in the electric current and the collapse of electric field 12,13 . This will stop the electric dehydrator from working and deteriorate the oil–water separation efficiency, seriously restricting the development and application of electrostatic demulsification technology.…”