多孔介质中甲烷水合物聚散过程的交流阻抗谱响应特征

电学特性实验是探索天然气水合物(以下简称水合物)生成分解过程及其动力学特征的有效技术手段。较之于过去单一的仅对电阻率参数进行测试的实验方法,交流阻抗谱测试方法可以获得一定频率范围内被测体系的阻抗(包括电阻、电抗)特性变化规律,从而有助于更全面深入地认识水合物的电学性质特征。为此,设计了甲烷水合物交流阻抗谱测试系统,以甲烷水合物一多孔介质一浓度为3.5%的盐水为研究体系,测试了水合物在多孔介质内合成与分解过程中研究体系的阻抗谱,并分析了阻抗谱特征参数随水合物饱和度变化的规律。结果表明:①采用激发源的不同频率测试的结果差异明显,在低测试频率(0.1~10.6 Hz)下,测试体系的水合物饱和度与阻抗谱参数之间未表现出明显的规律性关系,而在中高测试频率(101.8 Hz~1 MHz)下,阻抗谱参数随着测试体系水合物饱和度的增加而增加;②当测试频率为101.8Hz、1 114Hz和10 746 Hz时,在一定的误差允许范围内,测试体系的阻抗谱参数与水合物饱和度之间符合单调递增的线性关系;③阻抗幅值的频散特性与水合物饱和度之间存在着明显的对应关系。

Response characteristics of AC impedance spectroscopy during the formation and dissociation of methane hydrate in porous media

Electrical property test is an effective technique to identify the formation and dissociation process of natural gas hydrate (“the hydrate” for short) and to investigate its dynamic characteristics. The AC impedance spectroscopy testing method is better than the simple ones which only test resistivity parameters, for it can be used to test the variation rules of impedance (e.g. resistivity and reactance) of the tested system in a certain range of frequency. And thus, the electrical characteristics of hydrate can be understood further. In this paper, a system used to test impedance spectroscopy of methane hydrate was designed. Methane hydrate-porous media-brine of 3.5% was prepared as the object in this study. Then, its impedance spectrum was tested during the formation and dissociation of hydrate in porous media and the variation rules of characteristic parameters of impedance spectroscopy with hydrate saturation were analyzed. It is shown that the test results are significantly different when the frequency of excitation source is different. When the test frequency is low (0.1-10.6 Hz), there is no obvious relationship between the hydrate saturation and the impedance spectroscopy parameters of tested system. At middle- high test frequency (101.8 Hz-1 MHz), however, the impedance spectroscopy parameters rise with the increase of hydrate saturation. Besides, when the test frequency is 101.8, 1 114 and 1 0746 Hz, there is a monotonic increasing linear relationship between the hydrate saturation and the impedance spectroscopy parameters of the tested system within a certain range of allowable errors. And finally, there is an obvious correspondence between hydrate saturation and the frequency dispersion of impedance amplitude.