Collaborative Research: Shear Wave Studies of Hydrate Ridge, Oregon Continental Margin, During Planned ODP leg 198

Pecher 00- 02487 Trehu 00- 02410推荐项目是在大洋钻探计划（ODP）第198航次期间从钻孔中进行一系列地震实验，以绘制俄勒冈州海伯利脊沉积物中天然气水合物和游离气的分布图。 这些实验将从直接岩心描述、直接岩心测量和钻孔测井到周围沉积物中的观测结果进行扩展，从而在更大的沉积物体积上提供推断的天然气水合物和游离气赋存的3-D覆盖。 实验包括：1）具有固定源接收器的恒定偏移距垂直地震剖面（VSP），与零偏移距VSP配合，这将产生垂直连续的剪切波速度（Vs）剖面; 2）通过用第二艘船在井眼上方射击到井眼内固定深度处的接收器而获取的游离VSP，从而获得高质量的Vs和纵波（Vp）数据以校准含天然气水合物沉积物的岩石物理模型; 3）在一个钻孔周围部署密集阵列的海底地震仪，用于密集的3-D地震覆盖，以检查推断的聚焦流体通量的区域及其与天然气水合物盖的关系;以及4）在活塞部署期间使用ODP高级活塞取芯器（APC）作为地震源，用于使用OBS阵列进行更大阵列的测量。 这些地球物理结果将直接与钻井结果联系起来，以约束收敛边缘环境中流体通量、游离气体和水合物形成之间的关系。

Pecher 00-02487Trehu 00-02410Recommended project is for a series of seismic experiments to be conducted from boreholes during Ocean Drilling Program (ODP) Leg 198 to map occurrences of gas hydrate and free gas in sediments on Hydrate Ridge offshore Oregon. These experiments will geophysically extend observations from direct core description, direct core measurement, and borehole logging into the surrounding sediments, thereby provide 3-D coverage of inferred gas hydrate and free gas occurrence over a much larger sediment volume. The experiments include: 1) constant-offset vertical seismic profiling (VSP) with a fixed source receiver, coordinated with zero-offset VSP's, which will result in vertically continuous shear-wave velocity (Vs) profiles; 2) walkaway VSP's, acquired by shooting over the borehole with a second ship to a receiver at fixed depth within the borehole, thereby acquiring high-quality Vs and compressional wave (Vp) data to calibrate rock physics models of gas-hydrate bearing sediments; 3) deployment of ocean bottom seismometers in a dense array around one of the boreholes for dense 3-D seismic coverage to examine an area of inferred focused fluid flux and its relationship to a gas hydrate cap; and 4) using the ODP Advanced Piston Corer (APC) as a seismic source during piston deployment for a larger array of measurements using the OBS array. These geophysical results will be directly tied to drilling results to constrain relationships between fluid flux, free gas, and hydrate formation in a convergent margin setting.***