Experimental Study on Consolidation Behavior and Permeability Characteristics during Dissociation of Methane Hydrate by Depressurization Process
Experimental Study on Consolidation Behavior and Permeability Characteristics during Dissociation of Methane Hydrate by Depressurization Process
复制标题
甲烷水合物降压解离固结行为及渗透特性实验研究
DOI：
10.2473/journalofmmij.124.498
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
Tsutomu Yamaguchi
中科院分区：
文献类型：
--
作者：
Y. Sakamoto;Mai Shimokawara;K. Ohga;K. Miyazaki;T. Komai;K. Aoki;Tsutomu Yamaguchi
甲烷水合物（MH）是未来潜在的天然气资源之一，因为大量的甲烷水合物存在于世界范围内的海洋沉积物或多年冻土区。从产气量和经济性的角度来看，降压过程是MH原位解离过程中最有效的采气过程，但降压过程中有效应力的增加会导致MH沉积物固结和渗透率降低。因此，也有可能导致产气量下降。因此，了解MH储层中的行为，特别是在开发MH萃取系统以及考虑开发对环境的影响时，是非常重要的。在本研究中，我们使用特殊的装置对MH减压解离过程中的固结和产气行为进行了实验研究。为了再现真实的气体和水的流动情况，我们使用圆盘状样品作为模拟MH沉积物。构建了多孔介质中MH分离过程的水平径向流动，并采用垂直加载系统模拟了真实MH沉积物中的岩石压力条件。通过实验观察发现，在不同的温度和压力条件下，减压过程中的解离产气分为3个阶段：1)减压过程中甲烷气体在孔隙空间中的膨胀；2)由于砂粒和各相的潜热而解离；3)由于温度边界的热传导而解离。减压初期有效应力的增加是影响压实行为的主导因素，恒定有效应力条件下的变形主要取决于蠕变效应，而非MH解离作用。以解离压力、砂粒度、MH饱和度和初始温度为实验参数，探讨了这些参数对MH解离、固结和解离气产量的影响。
Methane hydrate (MH) is one of the potential resources of natural gas in the near future, because large amount of MH exists in marine sediments or in permafrost regions worldwide.Depressurization process is regarded as the most effective process for gas recovery from the viewpoints of gas productivity and economical efficiency, compared with the other in-situ dissociation processes of MH. However, increase of effective stress during depressurization causes consolidation of MH sediments and permeability reduction. As a result, decrease of gas productivity is also supposed. Therefore, it is very important to understand the behavior in MH reservoir, especially in developing the extraction system for MH, and when considering the environmental impacts due to the development. In this study, we conducted an experimental study on consolidation and gas production behavior during MH dissociation by depressurization, using the special type apparatus. To reproduce the real flow condition of gas and water, we used disc shape samples as simulated MH sediment. Horizontal radial flow in porous media during MH dissociation was constructed whereas vertical load system was used to simulate rock pressure conditions in real MH sediment.From an experimental observation, it was found that dissociation and gas production during depressurization consisted of the following three stages depending on temperature and pressure conditions, such as 1) expansion of methane gas in pore space by depressurization, 2) dissociation due to the latent heat of sand grain and each phases and 3) dissociation due to thermal conduction from outer temperature boundary. In addition, we confirmed that increase of effective stress at the initial stage of depressurization was dominant factor on compaction behavior, and deformation after constant effective stress condition was primarily dependent on the creep effect rather than MH dissociation.Then, dissociation pressure, sand grain size, MH saturation and initial temperature was changed as experimental parameters, we discussed the effect of these parameters on MH dissociation, consolidation, and dissociated gas production.