Theoretical modelling of the impact of free gas on seismic velocities

Sediments at the sea bottom of ten contain gas - normally methan, nitrogen or carbon dioxide (see f.i. Wheeler, 1986, Boden 1987). The presence of gas in a sediment affects its mechanical properties, and may thus have an impact on the stability of oil platforms resting on the sea bottom. Also, pockets of gas may cause dangerous situations during oil drilling, especially if the driller is not prepared for it. Seismic data often represent the only available information from the sediment prior to planning of platform sites, and drilling. Thus, it is important to be able to decide from the seismic data - with largest possible certainty - whether a sediment contains gas or not.