IMPROVEMENT IN IMAGING BELOW SHALLOWGAS CLOUD USING SEISMIC MULTIPLES

In Malaysian Basins, offshore Malaysia, there are many seismic imaging issues
related to the shallow anomalies so-called ‘gas cloud’ or ‘gas chimney’. Gas cloud
consists of gas bearing sediment, has always been a great challenge to acquiring good
seismic image of the subsurface. The seismic velocity field is severely complicated by
the presence of the gas-filled sediments, which produces strong multi-pathing and
complex travel time delays. The heterogeneous nature of these gas-filled areas results
in scattering, dispersion, internal multiples, mode conversion during wave propagation
through the heterogeneous zone and possibly inelastic losses. All these effects lead to
significant deterioration of the seismic image in terms of amplitude attenuation and
strong lateral variation of the seismic velocities.