Study on Gas Hydrate Formation-dissociation and Its Acoustic Responses in Unconsolidated Sands
Study on Gas Hydrate Formation-dissociation and Its Acoustic Responses in Unconsolidated Sands
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发表时间：
2008
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通讯作者：
Wang Jia-sheng
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作者：
Wang Jia-sheng
为了加深对天然气水合物在沉积物中的演化及其对松散沉积物的声学影响的认识，在0.18-0.28 mm的砂体中形成甲烷水合物并解离，并进行后续测试，以使声学特性和含水量能够用超声波检测和时域反射计（TDR）测量多轮实验的测试结果表明，天然气水合物的生成和分解都可以根据生成速度和分解速度分为三个阶段，通过对温度和压力数据的分析，结果表明，水合物首先在沉积物表面生成，在这三个分解阶段中，水合物的分解速度逐渐加快，声学特性表明，甲烷水合物在水合物含量为0-1%时具有胶结砂粒的能力当孔隙中不含水合物时，压缩速度急剧增加，声波衰减明显，而水合物作为孔隙流体的一部分形成，在饱和度为1%-1%时，超声信号消失。因此，该研究揭示了天然气水合物与沉积物颗粒的接触机制，为海洋地球物理勘探中地震信号的解释提供了新的思路。
To improve our understanding of the evolvement of gas hydrate in sediments and its acoustic impact on unconsolidated sediments,methane gas hydrate was formed and then dissociated in 0.18-0.28 mm sands,and subsequent testing was conducted to enable acoustic properties and water contents to be measured with ultrasonic detection and time domain reflectometry(TDR).The results of testing on several runs of experiments show that both of gas hydrate formation and dissociation could be divided into three periods according to formation speed and dissociation speed,respectively.Based on the analysis of temperature and pressure data,it comes to the conclusion that hydrate forms at the surface of sediments first and dissociates gradually fast during the three periods of dissociation.Moreover,acoustic properties shows that methane gas hydrates have the ability to cement sand grains at hydrate contents around 0-1% leading to a sharp increase in compression velocity and wave attenuation in specimens with no hydrate in the pore space.Whilst hydrates form as a part of the pore fluid and cause the blanking of ultrasonic signal appearing at the period of saturation 1%-90% during gas hydrate formation and dissociation.Consequently,this study reveals the contact mechanism between gas hydrate and sediment grains and provides a new idea to explain seismic signals in oceanic geophysical exploration.