超声探测技术在天然气水合物模拟实验中的应用

Application of Ultrasonic Detecting Technology in the Experimental Study of Gas Hydrate

为了解不同介质中天然气水合物的声学特性, 在特制的高压反应釜中分别进行了纯水、松散沉积物和岩心中甲烷水合物的生成和分解的模拟实验, 同时应用超声技术进行了探测。在纯水—甲烷体系中, 声波速度的变化主要受温度的制约, 水中生成的絮状水合物并没有使声波速度发生明显变化; 在纯水—松散沉积物—甲烷体系中, 声波速度和系统主频的变化灵敏地反映出体系内水合物的生成和分解; 在纯水—岩心—甲烷体系中, 随着水合物的生成, 纵波速度、横波速度以及纵波幅度均增大, 这说明纵波和横波的速度随着孔隙度的减小而增大, 而纵波幅度的衰减则随着孔隙度的减小而减小。实验结果显示, 超声探测是天然气水合物模拟实验中的一项有效的探测技术。

To understand the acoustic characteristics of gas hydrates in different media, the ultrasonic detecting technology is applied to the experimental study of gas hydrates in the pure water,the unsolidified sediment, and the core sample,respectively. The P-wave velocity is positively correlated with temperature linearly in the pure water, it means that the change of P-wave velocity is mostly caused by temperature but unobviously by the cotton-like gas hydrate formed in the water. In the long time experiment in the pure water,unsolidified sediments, and methane system, the change of P-wave velocity and characteristic frequency sensitively indicated the formation and dissociation of gas hydrate in the experimental system. The velocity of P wave and S wave, along with the amplitude of P wave, increased when gas hydrate formed in the pore water of the core sample. It is concluded that the velocity of P wave and S wave increase when the porosity of sample decreases, while the decay of the P-wave amplitude decreases. All the experimental results reveal that ultrasonic detecting technology is effective when it is applied to the experimental study of gas hydrate.