无机盐离子对石英表面油-水润湿性的影响

Effects of inorganic salt ions on the oil-water wettability of quartz surfaces

油藏岩石表面油-水润湿性对原油的开采具有重要影响,润湿性向亲水转变被认为是低矿化度水驱技术的主要机制,但是低矿化度水注入后岩石表面发生润湿性转变的微观机理目前依然存在很多争议.本研究针对极性分子在岩石表面的极性吸附,研究水中无机盐离子对石英表面润湿性的影响及其作用机理.研究发现,相同浓度下,NaCl溶液和KCl溶液的接触角基本相同;在浓度较低时,CaCl2溶液使三相接触角降低的幅度比NaCl溶液更大,Na2SO4溶液比NaCl溶液效果更明显;在较高浓度下,Na2SO4溶液的接触角与NaCl溶液相似.当离子浓度大到一定程度时,不同溶液的接触角都趋于15°左右,离子使吸附的极性分子基本都脱附,导致石英表面润湿性向亲水转变.基于石英粉末的Zeta电位测量和石英片表面的原子力显微镜(atomic force microscopy,AFM)粗糙度分析,提出了两种机理解释:(1)癸烷中的十八胺在油水界面质子化带正电,与水中阴离子相互吸引,降低了油水界面张力;(2)水中的阳离子在带负电的石英表面吸附,使石英片表面负电性减弱,并置换了部分石英表面吸附的十八胺分子,使石英表面亲油性减弱.

The oil-water wettability in reservoir rock plays an important role in the recovery of crude oil.However,the mechanism of wettability transition on reservoir rock surfaces after low salinity water injection is still controversial.In this paper,the influence of inorganic salt ions in water on the wettability of the rock surfaces with the adsorption of polar molecules and its mechanisms were studied.Amines commonly found in crude oil were selected to represent base polar components in oil,and a highly idealized experimental model was used to exclude the influence of various components and other effects in crude oil.By measuring the oil-water contact angle on the quartz surface,the influence of various salt ion concentration in water on the wettability of quartz in the presence of base polar molecule in oil was obtained,and the mechanism of wettability alteration was analyzed by Zeta potential and AFM measurement.The experiment result showed that,the cleaned surface of quartz was water-wet,when 0.1 mmol/L octadecylamine was added to decane,the contact angle rose to about 42°,that is,the surface of the quartz became more oil-wet.When salts with different kinds and concentrations were added to water,the water contact angles decreased sharply with the increase of the concentration of ions.The contact angles of NaCl solutions and KCl solutions were basically the same at the same concentrations.However,at low concentrations,the CaCl2 solutions reduced the contact angles more than the NaCl solutions.The contact angles of Na2SO4 solutions were smaller than those of NaCl solutions at low concentrations,while the contact angles of Na2SO4 solutions were similar to those of NaCl solutions at higher concentrations.When the ion concentrations reached a certain level,the contact angles of different solutions all tended to be about 15°,which indicated that the ions desorbed basically all of the adsorbed polar molecules,leading to the change of wettability of quartz surfaces to be water-wet.The clean quartz powder was highly electronegative when dispersed in pure water.After soaking in octadecylaminedecane,the surface of quartz powder was positively charged.As a contrast,the Zeta potential of the quartz powder after soaking in pure decane changed little,indicating that the potential change was caused by the adsorption of positive octadecylamine on the quartz surface.When the quartz powder soaked with octadecylaminedecane was reversely extracted into NaCl solution,the Zeta potential of the quartz powder would decrease,and the electropositivity would weaken.In high concentration NaCl solution,the Zeta potential of the quartz powder would quickly return to negative charge,indicating the desorption effect of ions in the solution on polar molecules.From the AFM roughness analysis,it can be seen that the surface roughness of clean quartz was small,after soaking in octadecylaminedecane,the roughness increased,indicating that octadecylamine was fully adsorbed on the surface of quartz.After the soaking of droplet,the surface roughness of quartz plate decreased,indicating that the partial desorption of octadecylamine under the effect of ions.Based on the Zeta potential measurement of quartz powder and AFM roughness analysis of quartz surfaces,two mechanisms were proposed:(1)The octadecylamine in decane adsorbed and protonated at oil-water interface,resulting in an electrostatic attraction with the anion,thus reducing the oil-water interfacial tension;(2)the cations in water could be adsorbed on the negatively-charged quartz surfaces,weakening the polarity of quartz surfaces and thus replacing part of adsorbed octadecylamine molecules on the quartz surfaces.