柴油污染粉土水油分布的核磁共振试验研究

Experimental Nuclear Magnetic Resonance Study of the Water and Oil Distributions in Diesel Contaminated Silt

为研究柴油污染粉土中水油两相在孔隙中的分布特征,利用低场核磁共振技术对人工制备的柴油污染粉土进行了室内试验研究.试验选用江苏宿迁地区粉土为试验土,选用0号柴油作为污染物,采用聚四氟乙烯圆筒作为制样模具和试样容器,采用压样法进行制样,利用MesoMR23-60H型中尺寸核磁共振成像分析仪测试试样.通过7组试验,对比研究了不同含水量、柴油含量和制样方法对柴油污染粉土的油水分布状态的影响.利用锰离子加快水弛豫的特性,其中3组试样的孔隙水中添加5 g/L氯化锰,刚好将油和水的信号区分开.由于锰离子浓度较小,可以忽略其对粉土中水分分布的影响.通过低场核磁共振得到柴油污染粉土的横向弛豫时间T2分布曲线,从微细观的角度分析了柴油污染粉土中柴油和水的孔隙分布规律.试验结果表明:适宜浓度的氯化锰可缩短油水两相体系中水的横向弛豫时间T2,从而分离水油信号;孔隙液为单相时,柴油比水更易优先占据大孔隙空间;当先加水后加柴油制样时,增加含油量会使孔隙液占据孔隙的孔径分布区间更加集中,孔隙液向较大孔径孔隙集中分布;先加柴油后加水制样时,柴油优先占据大孔径的孔隙,迫使后加入的水更易分布在较大孔径的孔隙.

In order to determine the water and oil distribution characteristics in diesel contaminated silt,manually made diesel contaminated silt specimens were experimentally studied in the laboratory.The test silt was collected from Suqian,Jiangsu province of China,and 0#diesel was used as the test diesel.All the silt specimens were statically compressed into a polytetrafluoroethylene(PTFE)column and then were characterized using a low-field nuclear magnetic resonance(NMR)spectrometer(MesoMR23-60H).The effects of different water content,diesel content,and specimen preparation methods on the oil-water distribution of diesel contaminated silt were studied using seven tests.Because Mn2+can accelerate the relaxation process of water,5 g/L MnCl2 solution was substituted for water in three specimens to obtain well separated NMR signals of pore water and pore diesel.As the concentration of Mn2+is relatively low,the effect of Mn2+on pore water redistribution in silt can be neglected.After measuring the T2 distribution curve of diesel contaminated silt via low-field NMR,the distribution of water and diesel in silt is discussed from the microscopic viewpoint.The results show the following:the appropriate concentration of MnCl2 can shorten the transverse relaxation time(T2)of water and separate mixed NMR signals of diesel and water in diesel contaminated silt;when the pore fluid consists of only water or diesel,the pore diesel prefers to occupy larger pores;when the specimen is prepared by adding water first and then diesel,increasing the diesel content will make the pore size distribution of pores occupied by fluid more concentrated and more pore fluid centrally distributed in macro pores;when the specimen is prepared by adding diesel first,the diesel initially enters into macro pores,which forces the postadded water to distribute in macro pores.