The Effect Of Changes In The Composition Of The Injected Water On The Charging Behavior Of The Liquid-solid Interface In The Reservoir

Low salinity water flooding can achieve higher acquisition rate relative to high salinity water flooding.Compared with traditional chemical flooding agent,it has the advantages of economy,environmental protection and easy operation.Low salinity water flooding is directed to the reservoir containing low concentrations of total dissolved solids?TDS?of water,and usually the salinity of injected water is less than 5000mg/L.At present,the mechanism action of low-salinity water flooding is mostly based on the idea of chemical flooding,such as the change of wetting property,the migration of particles,the decrease of interfacial tension and the increase of pH value and other physical and chemical results and has not yet deepened to the physical and chemical processes and its mechanism of action.It studies the change of charge composition about rock particles and crude oil emulsion surface,the relationship between liquid and solid surface charge changes and rock surface wettability and crude oil desorption by the conditions of changed brine composition in this paper.When the concentration of brine increases,the absolute value of Zeta potential of crude oil emulsion and rock solid surface decreases.When the ion concentration is the same,the effect of the divalent Ca²⁺ and Mg²⁺ ions on the Zeta potential is larger than that of Na⁺ and has a lower Zeta potential.When the ion concentration is 200mg/L,the Zeta potential increases with the increase of pH value in Sodium Chloride The absolute value of the Zeta potential increases first and then decreases with the increase of pH value in Calcium Chloride and Magnesium Chloride solution.For the simulated formation water,the presence of divalent ions has greater influence on the Zeta potential.The core slices of the saturated crude oil are soaked under different salt water conditions,the contact angle of the core slices is measured by the contact angle meter,and the change of the wet ability of the core slices is reflected by the contact angle.In Sodium Chloride,Calcium Chloride,Magnesium Chloride solution,the contact angle increases with the increase of the ion concentration.Under the same ion concentration,the contact angle of the core slice surface in the NaCl solution is smaller than that in the Calcium Chloride and Magnesium Chloride solution.When the ion concentration is 200mg/L,the contact angle of the surface of the core slice in NaCl solution decreases with the increase of pH.In Calcium Chloride and Magnesium Chloride solution,the pH value increases,the contact angle decreases first and then increases.For the simulated formation water,due to the presence of divalent ions,the reduction of the contact angle has a certain inhibitory effect.The amount of desorption of crude oil is determined by UV spectrophotometry.The desorption of crude oil on the rock surface is investigated by the amount of desorption.When the brine concentration increase,the amount of crude oil desorption decrease,and the inhibition of crude oil desorption increase.When the ion concentration is 200mg/L,in the Sodium Chloride solution,with the increase of pH value,the desorption amount of crude oil increases,and the increase of pH value promotes the desorption of crude oil on the rock surface.in the Sodium Chloride solution,the pH value increases,the amount of crude oil desorption increase first and then decrease.For the simulated formation water,the presence of divalent ions has a certain inhibitory effect on the desorption of crude oil on the rock surface.