Experimental Study on Methane Hydrate Accumulation from Dissolved Gas in Three-Dimensional Simulation Device

In order to obtain the knowledge of hydrate accumulating mechanism in seafloor, and lay the theoretical foundation for gas hydrate exploration and exploitation in the future, in this work, the formation of methane hydrate from dissolved gas was studied using a large three-dimensional accumulation device which was built by our laboratory to simulate the methane hydrate accumulation under the seafloor conditions. First, the real-time detection and analysis were made for the electrical resistivity and acoustic velocity changes at different positions over time during 80 days of methane hydrate formation experiments. The results show that hydrate formation affects the resistivity in different ways. At the beginning of the formation, the resistivity dropped continuously because of the salt-removing effect of hydrate formation which increases the salt concentration in the salt solution. In the late period of hydrate formation, the hydrates cement with particles of sediment making a sharp increase in resistivity. And then, the hydrate saturations in different sediment layers were determined from the experimental data on electrical resistivity using the modified Archie formula. The results demonstrate that the hydrate accumulates mostly in the middle and bottom of the sediment, but less in the upper space. This conclusion has also been confirmed through analyzing the variation of temperature in the sediment.