Abstract:

Compressional-wave impedance and shear-wave impedance of line USGS95-1 from Blake Ridge are obtained using elastic-impedance inversion method. Also, they are used to calculate Possion's ratio and Lame parameter of this line. All these elastic parameters are analyzed to identify the gashydrate sediments and free gas layer. The results show that the impedance and Lame parameter of the sediments containing gas hydrates are higher than those of the media with saturated water  at the same depth, but for free gas layer, these two kinds of elastic parameters, with Possion's ratio, become very low. Therefore, the gas-hydrate area and free gas area can be outlined respectively according to these characteristics. The zone of paralleling bottom with high impedance and Lame parameter indicates the gas-hydrate layer, and the area with low impedance and Possion's ratio trapped by gas-hydrate layer below it symbolizes the accumulation of free gas. The analysis also shows the main factor that causes the BSR of this line is the free gas below it.

Key words: elastic impedance, amplitude variation with offset, gas hydrate, Possion's ratio, Lame parameter