Study On The Influence Of Wettability Of Medium On Diesel Displacement By Surfactant

In recent years,with the substantial increase in the volume of petroleum extraction and by-product processing,the pollution of petroleum hydrocarbons in groundwater has become more serious.Due to their low solubility or even insolubility in water,once they leak into the underground environment,it is difficult to detect and repair.Therefore,the remediation of petroleum pollutants has become a hot topic in recent years,and in-situ flushing technology is a common repair method.Surfactants are commonly used in the remediation of groundwater petroleum hydrocarbons because they can effectively reduce the interfacial tension between oil and water.When the critical micelles concentration is reached,micelles will be formed effectively improving the solubility and fluidity of petroleum hydrocarbon,which is helpful for the remove of pollutants.Under natural conditions,the degree of wetting of underground media is different,which affects the migration and distribution of pollutants.Furthermore,the addition of surfactant will also have an effect on the wettability of medium.However,there is no systematic research on changes in media wettability caused by the addition of surfactants and their effects on pollutant migration and distribution.In this paper,diesel was used as a pollutant.From a microscopic perspective,the migration and distribution of diesel in different wetting media were studied using a visual micro-simulation device.Then,the displacement of diesel in groundwater was studied using a one-dimensional simulated sand column.The influence of media wettability on the displacement of diesel pollutants by surfactants was analyzed,and its change mechanism of medium surface properties was revealed.The experimental study reached the following conclusions:(1)The wettability of the quartz sand modified with dichlorodimethylsilane changes.As the amount of modifier increases,the larger the water-rock contact angle,the greater hydrophobic.Moreover,the modification of the medium combined by chemical bonds is relatively stable.As the wettability of the medium changes from strongly water-wet to oil-wet,the residual amount of diesel in the medium decreases first and then increases.Among them,the residual oil content in the intermediate-wet medium is the least with a water-rock contact angle of 76 °.(2)Wettability of the medium also have an effect on water migration.With the increase of the water wetness of the medium,the easier the flow of water,and the faster the flow speed in the pores of the medium.When the injection time and the amount of diesel are the same,the flow space of water decreases and the flow path becomes shorter,resulting the incomplete wetting of the medium.(3)Oil-wet media is favorable for the migration of diesel.And the migration speed of diesel is fast in strongly oil-wet medium.The displacement effect of diesel is poor in strongly water-wet and strongly oil-wet media.The intermediate-wet medium is benefit for the removal of diesel.(4)In the medium with contact angle of 0 °,the Zeta potential is negative,and the cationic surfactant is mainly adsorbed by electrostatic action.The large adsorption amount leads to a decrease of wettability and the Zeta potential of the surface of the medium,which is beneficial to the displacement of diesel.When the water-rock contact angle of the medium is 76 ° or more,the zeta potential is positive,and the cationic surfactant is mainly adsorbed by hydrogen bond and Vander Waals force.A small adsorption amount leads to an increase in the Zeta potential on the surface of the medium,and a decrease in oil wettability,which enhances the displacement of diesel.In the medium where the water-rock contact angle is equal to 76 °,the diesel removal efficiency is slightly reduced because of the increase of water wettability.(5)In a medium with a water-rock contact angle of 0 °,the Zeta potential of the surface of the medium is negative,and the hydrophobic end of the anionic surfactant is adsorbed on the surface of the medium mainly by hydrogen bonding and Vander Waals force.The small adsorption amount leads to a decrease of the zeta potential and wettability,which enhances the displacement of diesel.When the water-rock contact angle of the medium is 76 ° or more,the Zeta potential of the medium surface is positive,and the hydrophilic end of the anionic surfactant is mainly adsorbed on themedium surface by electrostatic action.The large adsorption amount leads to a decrease in the Zeta potential on the surface of the medium and an increase in oil wettability,which is unbeneficial for the displacement of diesel.Among them,it has lower displacement efficiency with a water-rock contact angle of 76 °.(6)Nonionic surfactants are mainly adsorbed on the medium by hydrogen bond and Vander-Waals forces.The small amount of adsorption results in a relatively small effect on the Zeta potential of the medium.When the water-rock contact angle of the medium is 0°,the nonionic surfactant can effectively increase the water-rock contact angle of the medium and enhance its displacement effect on diesel to a certain extent.When the water-rock contact angle of the medium is greater than 76 °,the injection of nonionic surfactant causes the decrease of the contact angle,which also enhances its displacement effect on diesel.Among them,the removal efficiency of diesel is more enhanced in the medium with a water-rock contact angle equal to 111 °,and the removal efficiency of diesel displacement is more reduced in the medium with a water-rock contact angle equal to 76 °.