Research On The Interface Properties Of Low Salinity Waterflooding

Low salinity water flooding is a new technology which is developed by BP research center and the university of Wyoming in 1996.It enhances the oil recovery by injecting brine whose salinity is lower than formation brine,and this technology is economical and environment-friendly.The study of low salinity water flooding is mainly focused on the interaction between injection water,formation fluid and reservoir rock,and the micro mechanism of oil/water/rock interface is emphasized.This research studied the influence of ion types and concentration on the wettability of rock surface and the interface property,including the law of charge change on the surface of rock/oil/clay mineral,and the influence of polar components on the wettability of rock surface is also studied.The innovation of this paper is measuring the change of interface properties under high temperature and high pressure conditions,including interface tension and contact angle test.Measuring Zeta potential of clay mineral,rocks and crude oil in different birne,we discovered that the divalent cation causes the surface of kaolinite and illite to be positively charged,resulting in the double electric layer attraction between oil/brine interface and brine/rock interface.The Zeta potential in Na+solution is negative and the absolute value is usually large.In Ca2+ and Mg2+ solution,its absolute value is usually smaller,even resulting in electrical inversion,the Zeta potential turns to positive value.The effect of calcium and magnesium on zeta potential is greater than that of sodium.The Zeta potential of reservoir rock in formation brine is relatively smaller than that in low salinity water and softened water.The Zeta potential of crude oil in brine is negative.Low salinity water converts interface forces of oil/water/rock from attraction to repulsion.Changing the concentration and type of ions changes the interfacial tension,but this change has no effect in low salinity water flooding.Measuring the contact angle of the surface of core section in different brine at different temperatures(60?100?140?)and pressures(20?30?40?50MPa),the change of wettability of core surface is reflected by the number.The contact angle in softened water is lower than that in formation brine at all temperatures and pressures.The contact angle in low salinity water(100 times diluted formation water)is lower than softened water.The contact angle of rock in the formation water with different dilution ratio becomes smaller first and then becomes larger,and there is a threshold value of the salinity of water.The contact angle increases with the increase of temperature,and the pressure has little effect.The contact angle of slabbed core in crude oil was measured with different polar components.The contact angle with the same aging time in CaCl2/MgCl2/Na2SO4 brine is larger than NaCl brine.The adsorption of asphalt has great influence on the wettability of rock surface.The longer the aging time in crude oil,the larger the contact angle.The surface of the core has a water film,which affects the adsorption of asphaltenes on the surface of the sandstone.The higher the concentration of brine is,the more obvious the decrease of adsorption is.