Abstract: The formation and dissociation of methane hydrate in subsea sediments were experimentally studied in porous media under simulated hydrate stability zone conditions for subsea hydrate resources.The changes of pressure,temperature and gas-production rate during hydrate dissociation were investigated under various conditions of hydrate formation and dissociation.The driving force (drawdown pressure) for hydrate dissociation was studied using a step depressurization procedure.The cumulative gas production rates under different depressurization modes were compared to reveal the mechanism of gas production in hydrate-bearing sediments.The experimental results show that the dissociation rate of hydrate mainly depends on the pressure drop.High pressure-drop can result in high dissociation rate and gas recovery.A minimum driving force is required for hydrate dissociation under certain temperatures.The cumulative gas production rate is related with the total pressure drop,but not affected by the depressurization modes.

Key words: methane, gas hydrate, hydrate formation and dissociation, hydrate resource, porous media, experimental study

摘要： 基于实际海洋水合物资源的赋存状态及温度、压力条件,在人工多孔介质中物理模拟海底水合物稳定带的水合物藏进行了水合物的形成与分解的实验研究。分析甲烷水合物在多孔介质中的形成与降压开采过程,揭示了其温度、压力和产气速率的变化规律。采用逐步降压的方法测定了多孔介质中水合物在特定温度下最小分解推动力,比较了不同降压模式下的累计产气量。结果表明,水合物形成过程中通过不断注水保持系统压力,甲烷可完全生成水合物,最终水合物藏中仅有水和水合物两相;实验条件下水合物的分解主要受压差影响,压差越大,分解速率越大,累计产气量越高;在一定温度下水合物的分解需有一个最小推动力。比较不同降压模式发现,累计产气量只与压差有关,而与降压模式无关。

关键词: 甲烷, 气体水合物, 水合物形成和分解, 水合物资源, 多孔介质, 实验研究