Study On The Effect Of Surface And Interface Properties On The Mechanical Behavior Of Micro-droplets In Oil-water Systems

Nearly 90% of onshore oil fields in China are developed through the water-injection method.As the oil fields gradually enter the later stage of high water cut development,oil-water mixtures are widely present in various production processes such as oil and gas extraction,mining gathering and transportation,and station treatment.Currently,the existing research on oil-water separation and demulsification mainly focuses on interface properties,demulsification mechanism,and optimization of separation device structure.This article conducts research from the perspective of the interaction between dispersed droplets and solid surfaces.Firstly,the effects of ion types and concentrations of the aqueous solutions on the thickness,refractive index and surface roughness of polyelectrolyte multilayers(PEMs)are studied,the reason why the internal structure and surface physical properties of PEMs change with the salt concentration in the aqueous environment is clarified,the mechanism of ion-specific effect of PEMs is revealed,and the influence of ionic strength on the underwater oil repellency of the PEMs is discussed.Secondly,study on the effect of surface structure on the mechanical behavior of dispersed droplets is conducted,the contact angle and adhesion force of oil droplets in water on different surface structures are measured,and the reason for the differences in contact angle and adhesion force on rough surface structures is analyzed.Compared with the improved Rumpf model and SRYL model,it is proved that the Van der Waals force calculation model based on refractive index can be effectively used to analyze the adhesion between dispersed droplets and solid surface.Subsequently,the dynamic behavior of core-shell drops on surfaces with different wettability in the air after contact between the air-water interface and the oil-water interface is investigated.It is clarified that the dynamic behavior of core-shell drops on lipophilic surfaces is the joint result of the combined force at the four phase contact line and the decrease in system energy.Based on Ohnesorge number,the influence mechanism of hydrophilic surface wettability and core-shell drop size on the droplet’s dynamic behavior is elucidated.At last,the influence of surface wettability of agglomeration plates on oil-water separation efficiency under different experimental conditions is studied through a loop and oil-water separation device.The improvement effect of agglomeration plate and coating modification on oil-water separation is analyzed.Combined with Fluent simulation,the influence and mechanism of surface wettability of agglomeration plates on oil-water separation under different inlet conditions is further studied.