南海神狐海域水合物一维速度结构研究:基于中—低饱和度水合物区的约束

Study of 1-D Velocity Structure of Hydrate in Shenhu Area,South China Sea:Based on the Constraints of the Hydrate Zone with Moderate to Low Saturation

高精度OBS探测作为目前研究水合物的常用技术手段,可以获取水合物矿体精细速度结构,在研究天然气水合物饱和度、水合物资源的预测与开发等方面具有重要指导意义。然而正演模拟OBS速度结构是繁琐漫长的过程,构建合理的初始模型是后续精细结构快速成像的重要前提。本研究基于全球18个已探明地震波速度的水合物区,分析了水合物矿体内纵波速度的共性特征和影响因素,拟合了水合物矿体带纵波速度与海水深度、沉积物厚度的经验公式。综合经验公式、OBS数据与多道地震剖面,建立了神狐水合物区横向均匀初始模型,并通过射线追踪与走时拟合模拟了神狐海域的一维纵波速度结构。结果表明,神狐水合物矿体带具有高纵波速度(1.83~1.92 km/s),游离气层具有低P波速度(1.60~1.70 km/s),此外,基于全球的水合物速度经验公式对神狐海域速度结构模拟具有重要参考意义,有望为获取神狐海域二维/三维精确速度结构提供可靠的初始模型,进而指导水合物精细勘察与资源评估。

As a common technical means of hydrate research,high-precision OBS surveys can obtain the fine-scale velocity structure of hydrate orebody,which is important for studying gas hydrate saturation,prediction and development of hydrate resources.However,forward simulation of OBS velocity structure is a tedious and time-consuming process,and constructing a reasonable initial model is an important prerequisite for subsequent fast fine-scale structure imaging.Based on data from18hydrate areas in the world where velocity structures have been identified,this study analyzed the common characteristics and influencing factors of P-wave velocity in hydrate orebodies,and obtained the empirical formula of P-wave velocity in hydrate orebody zone with seawater depth and sediment thickness.Based on the empirical formula,OBS data and multi-channel seismic profiles,an initial model of Shenhu hydrate area is established,and a one-dimensional P-wave velocity structure of Shenhu sea area is obtained by ray tracing and travel-time fitting.The results show that Shenhu hydrate orebody has high P-wave velocity(1.83-1.92 km/s),and free gas has low P-wave velocity(1.60-1.70 km/s).In addition,the empirical formula can serve as an important reference for the simulation of the velocity structure in Shenhu area,and it is expected to provide a reliable initial model for obtaining the two-dimensional/three-dimensional velocity structures in Shenhu sea area so as to guide fine-scale explorations and resource assessments of hydrate.