裂隙充填型水合物声学响应机理研究

Pore-filling hydrate and fracture-filling hydrate are two basic forms of hydrates in nature. At present, most of the fracture-filling hydrate saturation are estimated based on seismic and logging data. However, since fracture-filling hydrate shows significant anisotropy in marine sediments, it is difficult to select appropriate rock physics models and effective parameters for accurate estimation of the hydrate saturation and hydrate type identification. And due to the lack of laboratory simulation data, it is also difficult to study the influence mechanism of fracture on the acoustic response of hydrate. In this study, we intend to carry out simulation experiments of fracture-filling hydrate formation on the 2-D acoustic detection experimental equipment developed by laboratory. Experiments were carried out to investigate the development of different fractures with respect to anisotropy, and the acoustic characteristics during the experiment were probed to obtain the acoustic response of fractures to hydrate formation. At the same time, the micro-distribution pattern of fracture-filling hydrate was directly observed by high-precision CT technique. The formation, distribution and acoustic response mechanism of fracture-filling hydrate were discussed. Combining the rock physics model and the acoustic simulation data, the most effective identification method for fracture-filling hydrate is obtained. The research results will provide theoretical support for fracture-filling hydrate detection and scientific estimation of saturation.

孔隙充填型水合物和裂隙充填型水合物是自然界中水合物存在的两种基本类型。目前，国内外大多依据地震和声波测井数据估算裂隙充填型水合物饱和度，但由于裂隙充填型水合物在海洋沉积物中表现出显著的各向异性，难以选择合适的岩石物理模型和有效参数进行饱和度估算和水合物类型识别，探讨裂隙对水合物声学响应的影响机理。本项目拟在研发的二维声学探测实验设备上，开展裂隙充填型水合物形成模拟实验，针对各向异性开展不同裂隙发育情况实验，并探测实验过程中声学特性变化特征，获取裂隙对水合物形成的声响应特征，同时借助高精度CT技术对裂隙充填型水合物的微观分布模式进行直接观测，探讨裂隙充填型水合物的形成、分布和声学特性响应机理，结合岩石物理模型和室内声学模拟实验数据，获取裂隙充填型水合物的有效识别方法。研究成果将为裂隙充填型水合物探测和饱和度科学估算提供理论依据和支撑。

孔隙充填型水合物和裂隙充填型水合物是自然界中水合物存在的两种基本类型。目前，国内外大多依据地震和声波测井数据估算裂隙充填型水合物饱和度，但由于裂隙充填型水合物在海洋沉积物中表现出显著的各向异性，难以选择合适的岩石物理模型和有效参数进行饱和度估算和水合物类型识别，探讨裂隙对水合物声学响应的影响特征。本文在水合物岩心样品形成及测试系统和裂隙充填型水合物各向异性研究的声学特性测试实验装置中开展裂隙充填型水合物声学实验研究。并针对各向异性开展不同裂隙发育情况实验，探测实验过程中声学特性变化特征，获取裂隙对水合物形成的声响应特征。通过岩石物理模型和室内声学模拟实验，获取裂隙充填型水合物有效的识别方法，为裂隙充填型水合物探测和饱和度估算提供模型和参数支撑。主要结论是：裂隙充填型水合物声波速度随水合物含量的增大而增大，纵波实验结果与TIT层状介质模型拟合较好。裂隙充填型水合物层具有明显的各向异性，含水合物层纵波速度、横波速度与裂隙倾角和水合物含量有关。实验获取的纵波数据同理论模型具有较好的对应关系，能够反映不同裂隙发育倾角下不同水合物含量的声学特性。孔隙充填型水合物的密度速度属性曲线为正斜率，裂隙充填型则为负斜率，岩石物理模拟和实验模拟的结果趋势一致，因此基于密度速度属性识别孔隙充填型和裂隙充填型水合物具有可行性。