基于宽频电阻抗特性与阿尔奇公式的含水合物饱和度计算模型

A Calculation Model for Hydrate Saturation based on Broadband Electrical Impedance and Archie’s Formula

摘要:

以自主设计开发的水合物电学参数测量装置为基础，在频率范围5Hz~400kHz内测试了不同饱和度条件下的含四氢呋喃水合物海沙体系的宽频阻抗。分析了水合物生成分解过程中模拟沉积物的宽频阻抗特性，讨论了不同含水合物饱和度条件下的阻抗幅值频散特性及其与饱和度之间的定量关系，建立了基于宽频阻抗幅值和阿尔奇公式的含水合物饱和度计算模型。研究结果表明:（1）含水合物天然海沙体系的阻抗幅值呈现出频散特性，频散特性受到孔隙壁与孔隙流体之间界面极化效应的影响，阻抗幅值频散度与含水合物饱和度之间呈现近似线性关系；（2）在测试频率200~200kHz时，阿尔奇公式中的胶接指数较为稳定，饱和度指数与测试频率的对数之间呈现出近似线性的关系，测试频率应作为含水合物饱和度计算模型的参数。本研究为沉积物中含水合物饱和度的评价提供了新方法，通过测量宽频阻抗幅值并应用所提出的模型，综合多个频率的模型计算结果有望得到更加准确可靠的饱和度评价值。

Abstract:

Based on the self-designed equipment for measuring the electrical parameters of hydrate, the broadband electrical impedance of sea sand with tetrahydrofuran hydrate of different saturations was measured in the frequency range of 5Hz ~ 400 kHz. The broadband impedance characteristics of the simulated sediments during hydrate formation and decomposition were analyzed, and the dispersion characteristics of the impedance amplitude under different hydrate saturations as well as the quantitative relation between the impedance amplitude and saturation were discussed. A calculation model of hydrate saturation based on broadband impedance amplitude and Archie formula was established finally. It has been shown that: (1) the impedance amplitude of hydrate bearing sea sand system presents dispersion characteristics, which is affected by the interface polarization effect between the pore wall and fluid, and the relation between the impedance amplitude dispersion and hydrate saturation is approximately linear; (2) at the test frequency of 200 ~ 200kHz, the cementation index in Archie"s formula is stable and the relation between saturation index and logarithm of the test frequency is approximately linear; thus the test frequency should be used as a parameter of the hydrate saturation calculation model. This study provides a new method for the evaluation of hydrate saturation in sediment. By measuring the broadband impedance amplitude and applying the proposed model, it is expected to obtain a more accurate and reliable saturation value by integrating the model calculation results of multiple frequencies.