--> Abstract: Seismic Amplitudes and Low Gas Saturation: A Case Study from Green Canyon Block 474
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Previous HitSeismicNext Hit Amplitudes and Low Gas Saturation: A Case Study from Green Canyon Block 474

John O'Brien
Anadarko Petroleum Corporation, P.O. Box 1330, Houston, Texas 77251-1330

Previous HitSeismicNext Hit amplitude anomalies are a compelling direct hydrocarbon indicator but unfortunately cannot discriminate between high and low levels of gas saturation. This is demonstrated dramatically in the King Kong/Lisa Anne minibasin in the deep-water Gulf of Mexico. Both the King Kong and Lisa Anne features, located on opposing sides of the minibasin at the same stratigraphic level, Previous HitdisplayNext Hit very similar amplitude anomalies on migrated Previous HitseismicNext Hit volumes. However King Kong contains gas at commercial levels while Lisa Anne contains gas only at low saturation (5% - 25%). Wireline logs recorded at Lisa Anne show the presence of low saturation gas sands with low acoustic impedance, comparable to that of fully saturated gas sands. Thus the recorded Previous HitseismicNext Hit amplitude anomalies are valid, but indicate the presence of low saturation gas sands rather than sands with commercial gas levels.

Log Previous HitdataNext Hit document a complex distribution of pore fluids in the Lisa Anne sands with multiple low-gas-saturation and brine saturated sands stacked one above another. The Previous HitdataTop also show that sand bodies of considerable thickness can be charged with low saturation gas, in this case thicknesses in excess of 80 ft. The absence of a gas cap argues that this is a dynamic system which is not in hydrodynamic equilibrium; fluids have moved through the system in the recent past and possibly continue to do so at the present day.

 

AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana