基于宽频复电阻率的含黏土沉积物中水合物饱和度计算方法

天然气水合物沉积物中的黏土成分显著影响沉积物的电学特性以及水合物饱和度的计算模型。以自主设计开发的复电阻率参数测量装置为实验平台,在20 Hz ~ 100 kHz频率范围内测试了黏土条件下含水合物海沙体系的复电阻率,分析了复电阻率的频散特性、黏土影响以及主导的电极化机制,利用泥质修正Archie公式建立了基于宽频复电阻率的水合物饱和度计算模型。研究结果表明：（1）含水合物海沙体系的复电阻率呈现出显著的频散特性,双电层极化和界面极化分别是20 Hz ~ 1 kHz和1 ~ 100 kHz频段主导的极化机制;（2）黏土颗粒表面的双电层发生形变增强了含水合物沉积物双电层极化作用,提高了复电阻率相角和虚部的绝对值;（3）在20 Hz ~ 100 kHz频率范围内泥质修正Archie公式岩性系数较为稳定,而胶结指数和饱和度指数与测试频率之间的关系在20 Hz ~ 1 kHz和1 ~ 100 kHz频段差异显著,因此应分频段建立水合物饱和度计算模型。本研究为探讨含水合物沉积物的低频电学特性和建立含黏土沉积物中水合物饱和度计算模型提供了新的途径。

Calculation Method of Hydrate Saturation in Clay-Bearing Sediment Based on Wide-Band Complex Resistivity

The clay in gas hydrate sediments significantly affects the electrical properties of the sediments and the calculation model of hydrate saturation. The complex resistivity of hydrate-bearing sands with clay was measured in the frequency range of 20 Hz - 100 kHz based on a self-developed apparatus. The dispersion characteristics, the influence of clay and the dominant electrical mechanisms of complex resistivity were analyzed. A calculation model of hydrate saturation based on broadband complex resistivity was established by using the modified Archie formula. It was demonstrated that: (1) the complex resistivity of hydrate-bearing sands exhibited significant frequency-dispersion characteristics, and the polarization mechanism was dominated by double-layer polarization and interfacial polarization in 20 Hz - 1 kHz and 1 - 100 kHz, respectively; (2) the electrical-double-layer polarization of hydrate-bearing sediments was enhanced by the deformation of the electrical double layer on the surface of clay particles, resulting in an increase of the absolute values of the phase angle and imaginary part of complex resistivity; (3) the lithology coefficient in Archie formula was relatively stable in the frequency band of 20 Hz - 100 kHz, while the relationship between the cementation index and saturation index and frequency showed different characteristics in the frequency bands of 20 Hz - 1 kHz and 1 - 100 kHz, thus the calculation model of hydrate saturation should be established for different frequency bands. A new approach is provided for investigating the low-frequency electrical properties of hydrate-bearing sediments and establishing the calculation model of hydrate saturation in clay-bearing sediments.