The In-situ Displacement Method Was Used To Study The Relationship Between The Displacement Ability Of Several Demulsifiers And The Demulsification Performance

Produced liquid in oilfield usually exists in the form of emulsions.Chemical demulsification is the most commonly used technique for emulsion breaking.Demulsifiers are widely used in oilfield,but the demulsification mechanism of demulsifier has not been unified.At present,researchers believe that the mechanisms of demulsification include replacement mechanism,flocculation mechanism,phase inversion mechanism,solubilization mechanism and interface charge neutralization mechanism,etc.,among which replacement mechanism is well-accepted.However,a feasible approach to evaluate the replacement capacity has not been developed yet.And there is no direct evidence that the demulsifier displacement ability is positively correlated with demulsification performance.In the present study,a single-droplet in-situ displacement method has been established,and the corresponding experimental device has been built.The relationship between the capacity to replace natural emulsifier(asphaltenes and colloid)of several demulsifiers and their demulsification performance has been revealed,.which provides a reference for the deep understanding of the mechanism of demulsification and rapid screening of demulsifiers in oil field.In this work,the idea of single-droplet in-situ displacement was firstly proposed,and the formula for calculating the displacement area was obtained.The main variables in the formula include the demulsifier concentration(Ct)at different displacement times,the single molecule coverage area of the demulsifier and the saturated adsorption amount.The formula of demulsifier concentration required in the calculation formula was obtained through the on-line analysis system of fiber-optic evanescent sensor.A single-drop in-situ displacement evaluation device was built by using interface parameter integrated measurement system,peristaltic pump and magnetic stirrer.Then the displacement capacities of different demulsifiers and the effects of concentration and temperature on their displacement capacities were systematically compared using the single droplet in situ displacement evaluation device.The monomolecular coverage and saturated adsorption of four demulsifier(1#,2#,3#and 4#)molecules in the displacement formula were determined by interfacial tension experiments at different temperatures,With the increase of temperature,the saturated adsorption decreased and monomolecular coverage increased.We Found that when natural emulsifier(asphalt,colloid and asphaltene+glial)adsorb on the oil-water interface under the same condition,the replacement efficiency of demulsifier order is 3#>4#>2#>1#.Then the effects of different conditions on the efficiency of demulsifier replacement were discussed.It was found that the replacement efficiency of demulsifier increased with the increase of demulsifier concentration,and the replacement efficiency of 3#that is the best among the four investigated demulsifer,could reach 286%under the experimental condition.There is an approximated linear relationship between replacement efficiency and demulsifier concentration.With the increase of temperature,the displace efficiency of demulsifiers slightly increased,which indicated that the concentration of demulsifier should be the dominant factor that influenced the displace efficiency.Finally,the performance of the demulsifier for different oil samples was evaluated.For crude oils with high asphaltene content(6.78wt%and 9.87wt%),the order in performance of demulsifier used in this study is 3#>4#>2#>1#,which is in agreement with the replacement ability of demulsifier.For crude oil with low asphaltene content(1.94wt%),the order in performance of demulsifier 1#>2#>3#>4#,which is inconsistent with the replacement ability of demulsifier.The results indicated that the positive relationship between displacement and demulsification performance is related to the asphaltene content in crude oil;Demulsifier demulsification performance is better with the increase of temperature and demulsifier dosage,which is consistent with the change rule of the demulsifier displacement ability.