南海北部陆坡天然气水合物的地震速度研究

Study of Seismic Velocity about Gas Hydrates in the Northern Slope of the South China Sea

采用D ix公式法和速度反演法分别对南海北部陆坡测线A和B的层速度及纵波速度进行计算,结合BSR、振幅空白带以及波形极性反转等多种水合物赋存信息的分析,对水合物成矿带的速度特征进行了综合研究。结果表明:低速背景中的高速异常,是天然气水合物赋存的重要特征;高速异常体一般呈平行于海底的带状分布;在高速异常体的内部,速度也是不断变化的,一般在异常体的中心速度最高,由中心到边缘速度逐渐降低,反映在水合物矿带内部,水合物饱和度由矿体中心向边缘逐渐降低的特征。研究结果表明高精度速度分析不仅可以帮助寻找水合物矿点,还可以进一步判定水合物的富集层位。

The interval velocity and P velocity of seismic profiles A and B in the northern slope of the South China Sea were calculated by the methods of Dix equation and velocity inversion. The velocity characteristics of the gas hydrate bed were studied in detail based on the calculated results and the information, including BSR, amplitude blanking and polarity reversion of the waveform. It is shown that the higher velocity zone in the lower velo-city background is an important characteristic of gas hydrate bed, and that the higher velocity zone usually para-llel the seafloor, and that the velocity changes gradually in the higher velocity zone with the highest velocity at the center whereas the lowest at the margin, suggesting that the saturation of gas hydrate zone decreases gradually from the center to the margin. The study reveals that the high resolution velocity analysis is useful not ordy to search the hydrate spot but also to estimate the rich layer of gas hydrates.