【作者】 张剑；

【导师】 业渝光；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2008， 博士

【摘要】 作为一种极有潜力的化石能源-海洋天然气水合物日益受到人们更多的关注。目前,海洋地球物理勘探技术仍是海洋天然气水合物勘探和开发的主要技术,具有经济和高效等特点。海洋沉积物中水合物饱和度与声学特性关系是水合物地球物理探测技术的基础。天然气水合物是怎样改变地震波的传播,我们对此了解得还很不够。关于多孔介质中声波速度与水合物饱和度的关系,已经有一些理论模型。然而,在同一地区用不同的理论和模型得出的结果却有很大的不同,这就需要进行实验验证和参数分析以确定模型使用的适用性。在实验室中,模拟自然环境中天然气水合物赋存的条件,测量多孔介质中不同水合物饱和度情况下的声波速度,并研究两者之间的关系,可为水合物实际地震勘探数据采集、处理和解释,圈定含水合物沉积层的范围,估算天然气水合物的蕴藏量等方面提供指导意见,在方法和应用研究上具有重要意义。本文研制了一套实验装置,将超声技术和时域反射(TDR)技术结合,可以同时测量多孔介质中水合物的饱和度与声波速度等参数。使用该装置在固结人工岩心以及松散沉积物中进行了共计58个轮次的天然气水合物生成和分解实验,得到了可靠的实验结果。实验中温压、超声和TDR探测水合物的生成和分解均十分灵敏,而且,三种方法所探测到的生成点、分解点吻合,这说明利用超声技术和TDR技术联合探测多孔介质中水合物的饱和度与声速是十分有效的。实验得出了固结人工岩心中水合物饱和度与声波速度(包括纵波速度Vp和横波速度Vs)的关系,并使用实测的实验数据对时间平均方程、伍德及其修正方程、李权重方程和BGTL理论等常用的水合物饱和度估算模型进行了验证。实验结果表明,李权重方程和BGTL理论的速度预测值与实验值比较吻合,有广泛的适用性。对于李权重方程中W和n的取值、BGTL理论中G和n的取值在文中分别给出了一些建议,可以为两模型的实际应用提供一些参考。实验发现,水合物饱和度对沉积物声学特性的响应关系十分复杂,单一的模型或模型中参数的单一取值方式可能并不能完全适应所有的应用实例。在本实验人工固结岩心中天然气水合物赋存的微观模式,是颗粒接触模式或胶结模式。而在松散沉积物实验中,水合物先依附于沉积物骨架生成,并胶结了骨架颗粒,之后水合物开始在沉积物孔隙中以悬浮状形态生成。虽然本文实验中使用的材料与实际的海洋沉积物存在差别,但是得到的实验结果仍具有一定的指导意义。在掌握实验技术的基础上,使用实际的海洋沉积物岩心进行同样的实验,研究水合物饱和度与声学参数的响应关系,确定各理论方程中参数的取值,将得到实际的应用。更多还原

【Abstract】 Marine gas hydrate, potential fossil energy resources, has attracted more and more attention. As an economic and effective technique, marine geophysical survey is still the primary explorative technology at present. Relationship between gas hydrate saturation and acoustic characteristics in marine sediments is the foundation of geophysical exploration. However, it’s unclear how gas hydrate affect seismic wave.There are many existing models to describe the relationship between acoustic velocities and gas hydrate saturation. However, different models used in the same area may bring on different results. It’s necessary to confirm the legitimacy of the models and get an approach to use them correctly.Interpretation of seismic data, afterward locating of gas hydrate and estimation of resource require to understand the relationship between physical properties and saturation in gas hydrate-bearing sediments.An experimental apparatus was developed in the thesis. The apparatus combined high precision ultrasonic detection with Time Domain Reflectometry (TDR) in the same experimental apparatus to study the relationship between gas hydrate saturation and acoustic characteristics. Gas hydrate was formed and dissociated in artificial core and unconsolidated sediments for 58 experimental runs. Ultrasonic and TDR can detect the formation and dissociation of gas hydrate in porous media sensitively. The results show the experimental method is very effective.Relationship between gas hydrate saturation and acoustic velocities (including Vp and Vs) in consolidated artificial core was gained. Observed data in experiments was compared with the calculated data by time-average equation, Wood’s equation, Lee’s weighted equation and Biot-Gassmann Theory by Lee (BGTL). It suggests that the Lee’s weighted equation and BGTL are more applicable in our experiments and various sediments. The thesis also gave some instructive advices about the selection of W, n and G, n values in Lee’s weighted equation and BGTL.Experimental results revealed that the relationship between gas hydrate saturation and acoustic characteristics in sediments is quite complicated, and single model or parameter can’t be applicable for all situations. It is indicated that the micromodels of gas hydrate formed in the artificial core are grain contact model or cementation model in our experiments. However gas hydrate is formed firstly on the skeleton and cement the granules in unconsolidated sediments experiments, afterward they grow suspending in the pore space.Although the physical characteristics of experimental materials are different from them of actual marine sediments, the experimental results can direct practical application in some sense. Actual marine sediment cores will be used in similar experiments to study the relationship between gas hydrate saturation and acoustic parameters. Parameters of the models determined by experiments will be useful in practical application.更多还原