--> Abstract: Stratigraphic Traps in Deepwater Turbidite Reservoirs at the Base of Depositional Slope, by Joesph R. Straccia and Brad E. Prather; #90914(2000)

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Joesph R. Straccia1, Brad E. Prather1
(1) Shell International Petroleum, Rijswijk, Netherlands

Abstract: Stratigraphic Traps in Deepwater Turbidite Reservoirs at the Base of Depositional Slope

Significant hydrocarbon accumulations are stratigraphically trapped in deep-water turbidite reservoir sands that were deposited near the base of depositional slopes. These traps type represent a major global exploration (growth) opportunity for industry in deepwater. Improvements in drilling, completing and producing in water depths greater than 2000 m are opening up stratigraphic play opportunities which were not feasible just several years ago.

The break in slope onto the basin floor provides a key setting for the deposition of laterally continuous turbidite sands. Reservoir geometries here vary between sheet sands and amalgamated channels or combinations of both. Pinchout of reservoir sands or onlap onto the slope form the updip stratigraphic components to these traps. Leakage of hydrocarbons through thief zones within slope drapes and turbidite feeder systems connected to reservoirs at the toes-of-slopes probably represent the main trap risk in this setting. Cut-off of these thief zones results from faulting, slumping, submarine erosion, and shale plugging. Lateral and downdip trapping elements include sand pinchouts, truncation against salt or shale diapirs, monoclinal dip or faulting.

There is clearly no single trapping model, which is appropriate for all regions with toe-of-slope trap potential. There are, however, a certain number of common attributes which appear to be key to the formation of these traps. Diagnostic criteria such as trapping mechanism components, seismic scale reservoir architecture, and degree or lack of amplitude support are critical to the assessment. The fact that all the traps are not identical is encouraging from the standpoint that many combinations of mechanisms can lead to sizeable accumulations in this toe of slope setting.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana