油包水型原油乳状液核磁共振T2谱特征与形成机理分析

Characteristics and Generation Mechanism of NMR T2 Spectrum of W/O Crude Oil Emulsion

为认识油包水型原油乳状液核磁共振T2谱中各峰的形成机理,采用低场核磁共振CPMG自旋回波法测量了不同含水率的油包水型原油乳状液,分析了油包水型原油乳状液的T2谱特征,探讨了T2谱中各个峰的形成机理,并通过含Mn Cl2·4H2O油包水型原油乳状液的核磁共振实验进行了验证。结果表明:油包水型原油乳状液T2谱中存在三个峰,连续相中的原油发生自由流体弛豫形成T2A峰,被油束缚在分散相水滴表面的水发生表面流体弛豫形成T2B峰,远离液滴表面液滴内部的水发生自由流体弛豫形成T2C峰;含Mn Cl2·4H2O油包水型原油乳状液的T2谱中含有两个峰,未受Mn Cl2·4H2O影响的原油自由弛豫形成T2N峰;Mn Cl2·4H2O使水的自由弛豫和表面弛豫时间缩短,共同形成T2M峰,验证了原油乳状液T2谱中各个峰的弛豫机理分析。这些结果为利用低场核磁共振T2谱深入研究原油乳状液的性质奠定了基础。

In order to cognize the generation mechanism of the peaks in NMR T2 spectrum of W/O(water in oil)crude oil emulsion,the method of low-field NMR(nuclear magnetic resonance)CPMG(Carr-Purcell-Meiboom-Gill)spin-echo was used to measure the W/O crude oil emulsions with different water content,and the characteristics of T2spectra were analyzed.The formation and change mechanism of the peaks in NMR T2 spectra was presented,and then it was validated by the NMR experiment of W/O crude oil emulsions containing MnCl2·4H2O.The results showed that:There were three peaks in the T2 spectrum.The T2Apeak was from the free fluid relaxation in the continuous phase of crude oil.The surface fluid relaxation occurred in the water on the surface of droplets in dispersed phase bound by the oil,and the T2B peak was formed.The free fluid relaxation occurred in the water away from the surface of the droplet,and the T2C peak was formed.T2 spectrum of W/O crude oil emulsion containing MnCl2·4H2O had two peaks.The T2N peak was from the free relaxation of crude oil that was not affected by MnCl2·4H2O,and the process of free relaxation and surface relaxation in water sped up by MnCl2·4H2O formed the T2M peak,which verified the relaxation mechanism of the peaks in T2 spectra of the crude oil emulsions.These results lay a foundation for further study on the properties of crude oil emulsion by low-field NMR T2 spectra.