Application of spectral decomposition to detect deepwater gas reservoir

Summary In this paper, spectral decomposition techniques are applied to deepwater seismic data from Gulf of Mexico to examine the gas associated spectral anomalies. In the first case, thick gas sand with nearly constant P-impedance is encased in shale with non-symmetric P-impedance, and gas reservoir are bright at low-frequency iso-frequency sections; Commercial gas sand and low-gas saturated sand also show apparently different spectral characteristics. In the second case, gas reservoir includes two consecutive up-fining sand intervals with gradually changed P-impedance in each sand interval. Spectral anomalies of gas sand occur at high- frequency iso-frequency sections. Detailed forward modeling is analyzed to help understand the underlying physical mechanisms. Reservoir thickness and P- impedance structure are the first order factors to control the spectral decomposition responses of the above two gas reservoirs. Systematic synthetic model based on reservoir properties is needed to select optimal frequency range to directly detect hydrocarbon for specific reservoir.