Study On The Stability Of O / W Emulsion Based On Optical Tweezers Technology

In recent years, the produced sewage quantity in oil field increase with the continuous exploitation. Efficient treatment with oilfield wastewater has become one of the major technical problems that urgently need to be overcome. The key of oilfield wastewater treatment is breaking O/W emulsion. Therefore, the study on the stability of O/W emulsion is significant for breaking emulsion operation.Currently, the traditional measurement methods for emulsion stability are mostly focused on macro approach. The optical tweezers is a new method to determine the stability of the emulsion at the micro-level, which has the characteristics of non-contact, non-invasive manipulation for the particles. This work employed the simulated O/W emulsion as the main study object, observe the artificial induced collisions between particles at the micro-level with the help of optical tweezers and investigate the influence of asphaltene, resin, ring acid, surfactants, polymers and other factors on O/W emulsion stability. Meanwhile, the reliability of the optical tweezers related method was confirmed by measuring the effect of the above factors on the Zeta potential, Interfacial tension.Based on the statistics for two droplet collision probabilities, this work established the optical tweezers based research method (OTM) for O/W emulsion stability. The detailed operation conditions are60times water immersed objective,0.25w laser intensity, the general slide with the contact angle of40.55°and the dispersion medium of0.6mol/L NaCl. The experiment results are as follows:(1) OTM experiment shows that asphaltenes and resins contribute to the stability of O/W emulsions. However, naphthenic acid could not improve the stability of O/W emulsion. The overall result shows that asphaltenes have largest influence on the stability of O/W emulsion. The Sticking probability (SP) reduce from0.41to0.21when the mass fraction of asphaltenes increase from0.01%to0.2%. The addition of surfactance and HPAM will reduce the value of SP and increase the stability of O/W emulsions.(2) The result of Zeta potential is accordance with OTM. The absolute value of Zeta potential of emulsion formation by asphaltenes and water is the biggest, which indicated that asphaltenes have largest influence on the stability of O/W emulsion. The absolute value of Zeta potential increases with the increase of polymer concentration, molecular weight and degree of hydrolysis. It also increases as the concentration of dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) increases. While the concentration of OP-10has little influence over it. In a conclusion, Zeta potential could not evaluate the stability of O/W emulsions. However, OTM can evaluate the stability of O/W emulsions at the micro level.(3) The result of the interfacial tension is accordance with OTM. With the increase of the mass fraction of asphaltene and resin, interfacial tension decreases. However, as the increase of the mass fraction of naphthenic acids, the interfacial tension increases. As the concentration of OP-10, SDS, CTAB increasing, interfacial tension value decreases. With the concentration of polymer increasing, interfacial tension decreases. With the molecular weight and the degree of hydrolysis of polymer increasing, interfacial tension increases. Although low interface tension will improve the stability of emulsions, it is not the critical factor. However, OTM can evaluate the stability of O/W emulsions at the micro level.The overall results show that OTM is a newly and accurate method to evaluate the stability of emulsions. OTM can evaluate any emulsions no matter ion or non-ion surfactance at the micro level.