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Amplitude Analysis within a Sequence Stratigraphic Framework--Neogene Strata of Offshore Louisiana

PACHT, JORY A., ROBERT O. BROOKS, BRUCE E. BOWEN, and BERNARD L. SHAFFER, Calibre Consulting Services, Inc., Houston, TX

An approach to seismic interpretation, which combines analysis of depositional sequences, seismic facies, and reflection attributes is one of the most effective ways to explore for hydrocarbons in Neogene strata of offshore Louisiana. The variables that create amplitude anomalies are better understood when they are evaluated relative to specific facies of specific systems tracts.

Basin-floor fans commonly show a single reflector that downlaps onto the sequence boundary. They contain thick sands. The basin-floor fan systems tract is the most productive per unit volume of sediment in the study area. However, amplitude anomalies may not be present. Lowstand slope-fans exhibit concave-upward reflections

associated with reflections that downlap away from them (channel-levee facies), continuous to discontinuous reflections (overbank facies), chaotic reflections and thin parallel units. This is the most productive systems tract in the Gulf Coast. Good reservoirs are present in channels and nearby levees. Individual amplitude anomalies associated with them may be spatially small relative to reserve size.

Reflections in lowstand prograding-wedges exhibit divergence toward downthrown sides of growth faults. Good reservoir sands occur in prodelta-turbidite and delta-font facies. Strong bright spots are most often observed in this systems tract. Both transgressive and highstand systems tracts generally exhibit concordant reflections. Reservoir quality is generally poor in these systems tracts and many amplitude anomalies are not associated with producible hydrocarbons.

The likelihood of gas saturation can be most accurately ascertained when an integrated approach to direct hydrocarbon detection is undertaken.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)