Based on analysis of variation of elastic properties of natural gas and formation water under reservoir conditions

calculation of compressional velocity and shear velocity through gas-bearing strata

and physical si-mulation and experimental analysis

it is believed that gas-bearing strata are characterized by the following seismic responses: compresional velocity of gas with larger specific gravity is higher than that of gas with smaller specific gravity;compresional velocity in rocks containing saline water increases with increasing water salinity;and fluid properties have relatively large influence on compressional velocity

but have little influence on shear velocity.There would be a certain different seismic responses in strata bearing different fluids.Reflected energy in gas-bearing strata is relatively strong

while that in water-bearing strata is relatively weak.Seismic response in he-terogeneous gas-bearing strata would be characterized by relatively well developed diffracted wave.